Class 12 : Chemistry (English) – Chapter 4: The d- and f-Block Elements

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On June 25, 2025

EXPLANATION & SUMMARY

✨ Introductio
🔵 The d-block elements lie in the middle of the periodic table (Groups 3–12) and are also called transition elements because they show transition in properties from highly reactive s-block to less reactive p-block.
🟢 The f-block elements are placed separately at the bottom as lanthanoids (Z = 58–71) and actinoids (Z = 90–103), forming the inner transition elements.
🟠 These two blocks are important because they contribute to metallurgy, catalysis, alloys, electronic devices, and nuclear chemistry.

🌿 The d-Block Elements
🔹 Position and Electronic Configuration
💡 General electronic configuration: (n−1)d¹–¹⁰ ns⁰–²
✏ Example: Sc (Z=21) → [Ar] 3d¹ 4s²
➡ Key points:
In d-block, last electron enters (n−1)d orbital.
Variable oxidation states arise because both (n−1)d and ns orbitals have comparable energies.
Transition elements: those d-block elements that have partially filled d orbitals in their ground state or in common oxidation states.

🔹 General Characteristics
🧪 1. Variable Oxidation States
Due to similar energy of (n−1)d and ns orbitals.
Mn shows maximum (+2 to +7).
Stability depends on lattice enthalpy, hydration enthalpy, and electronic factors.
⚡ 2. Formation of Coloured Ions
Colour due to d–d transitions (electronic transitions between split d-orbitals in presence of ligands).
Colour intensity depends on ligands (Crystal Field Theory).
🔴 3. Catalytic Properties
d-block metals act as catalysts because they:
Can change oxidation states.
Provide surface for adsorption.
Examples: V₂O₅ in Contact process, Fe in Haber process.
🟡 4. Magnetic Properties
Paramagnetism due to unpaired d electrons.
Magnitude of magnetic moment (μ) = √(n(n+2)) BM (n = no. of unpaired e⁻).
Some compounds (like Mn²⁺, Fe³⁺) are strongly paramagnetic.
🔵 5. Alloy Formation
Close atomic sizes allow atoms to substitute each other.
Examples: Steel (Fe + C + others), brass (Cu + Zn), bronze (Cu + Sn).
🟢 6. Formation of Complex Compounds
Strong tendency to form complexes due to:
Small cationic size,
High nuclear charge,
Availability of vacant d orbitals.
Example: [Fe(CN)₆]³⁻, [Cu(NH₃)₄]²⁺.

🔹 Periodic Trends
💡 Across period (3d → 4d → 5d → 6d series):
Atomic radii: Decrease → slight increase due to electron–electron repulsion and lanthanoid contraction.
Ionisation enthalpy: Generally increases left to right.
Standard electrode potential: Depends on stability of oxidation states.

🔹 Group-wise Highlights
🟦 Group 3 (Sc, Y, La, Ac)
Show +3 oxidation state, form colourless ions.
🟩 Group 4 (Ti, Zr, Hf)
Stable +4 state.
TiO₂: Photocatalyst, used in paints.
🟨 Group 5 (V, Nb, Ta)
Exhibit +5 stable state.
V₂O₅: Catalyst in Contact process.
🟧 Group 6 (Cr, Mo, W)
Cr: +3 and +6 stable.
K₂Cr₂O₇: Oxidising agent.
🟥 Group 7 (Mn, Tc, Re)
Mn shows oxidation states +2 to +7.
KMnO₄: Powerful oxidising agent.
🟪 Group 8–10 (Fe, Co, Ni, Ru, Rh, Pd, Os, Ir, Pt)
Ferrous metals → important in metallurgy.
Fe: Forms haemoglobin.
Pt, Pd: Catalysts in hydrogenation.
🟫 Group 11 (Cu, Ag, Au)
Known as coinage metals.
Stable in +1 oxidation state.
Cu²⁺, Ag⁺ form coloured complexes.
⬛ Group 12 (Zn, Cd, Hg)
Show +2 state.
Filled d¹⁰ configuration → not true transition metals.
Hg forms amalgams.

🌿 The f-Block Elements
🔹 General Features
💡 f-block includes lanthanoids and actinoids.
General configuration: (n−2)f¹–¹⁴ (n−1)d⁰–¹ ns².
Placed separately to keep periodic table structure intact.

🔹 Lanthanoids (Z=58–71)
🟦 Common oxidation state: +3.
🟩 Gradual decrease in atomic size with increase in atomic number = lanthanoid contraction.
Cause: Poor shielding of f-electrons.
Consequences:
Similar properties among lanthanoids.
Difficulty in separation.
Contraction affects d-block (Zr and Hf size almost same).
💡 Uses of Lanthanoids
CeO₂: Oxidising agent, used in polishing glass.
Mischmetal (La + Ce + others): In lighter flints.
Nd: In lasers, magnets.

🔹 Actinoids (Z=90–103)
🟨 Show wide range of oxidation states (+3 to +6, sometimes +7).
🟧 Strongly paramagnetic due to 5f electrons.
🟥 Show actinoid contraction (similar to lanthanoids).
🟦 Most actinoids are radioactive.
💡 Important examples
Th, U, Pu → nuclear fuels.
Am, Cm → artificial elements used in research.

🔹 Comparison of Lanthanoids and Actinoids
🟢 Lanthanoids: Mostly +3 oxidation state, less variable.
🔵 Actinoids: More variable oxidation states.
🟠 Lanthanoids: Mostly stable, few radioactive.
🔴 Actinoids: Mostly radioactive.
💡 Both: Show contraction due to poor shielding of f-electrons.

📝 Summary
d-Block
d-block lies in groups 3–12, general config (n−1)d¹–¹⁰ns⁰–².
Properties: Variable oxidation states, coloured ions (d–d transitions), catalysis, paramagnetism, alloy formation, complex formation.
Trends: Atomic size decreases across, slight irregularities due to lanthanoid contraction.
Important compounds: KMnO₄, K₂Cr₂O₇, TiO₂, Cu²⁺ complexes, coinage metals.
f-Block
f-block → lanthanoids + actinoids, general config (n−2)f¹–¹⁴(n−1)d⁰–¹ns².
Lanthanoids: Stable +3 oxidation, lanthanoid contraction → similar properties. Uses: CeO₂ (polishing), mischmetal, Nd magnets.
Actinoids: Variable oxidation states, radioactive, nuclear fuels.
Actinoid contraction similar to lanthanoid contraction.
Comparison
Lanthanoids: Limited oxidation variability, mostly non-radioactive.
Actinoids: More oxidation variability, mostly radioactive.
Both show contraction, complex formation, paramagnetism.

🎯 Quick Recap
🟢 d-block: Variable oxidation states, coloured ions, catalysts, alloys.
🔵 Lanthanoids: +3 state, contraction, polishing, magnets.
🟠 Actinoids: Radioactive, nuclear fuels, wide oxidation states.
🔴 Both: Contraction → similar sizes, strong complex formation.

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QUESTIONS FROM TEXTBOOK

Question 4.1
Write down the electronic configuration of:
(i) Cr³⁺ (ii) Pm³⁺ (iii) Cu⁺ (iv) Ce⁴⁺ (v) Co²⁺ (vi) Lu²⁺ (vii) Mn²⁺ (viii) Th⁴⁺
Answer
💡 Rule: Remove ns electrons first, then (n−1)d / (n−2)f.
🔵 Cr³⁺: Cr = [Ar] 3d⁵ 4s¹ → Cr³⁺ = [Ar] 3d³
🟢 Pm³⁺: Pm = [Xe] 4f⁵ 6s² → Pm³⁺ = [Xe] 4f⁴
🟠 Cu⁺: Cu = [Ar] 3d¹⁰ 4s¹ → Cu⁺ = [Ar] 3d¹⁰
🔴 Ce⁴⁺: Ce = [Xe] 4f¹ 5d¹ 6s² → Ce⁴⁺ = [Xe]
🟡 Co²⁺: Co = [Ar] 3d⁷ 4s² → Co²⁺ = [Ar] 3d⁷
🔷 Lu²⁺: Lu = [Xe] 4f¹⁴ 5d¹ 6s² → Lu²⁺ = [Xe] 4f¹⁴ 5d¹
🔶 Mn²⁺: Mn = [Ar] 3d⁵ 4s² → Mn²⁺ = [Ar] 3d⁵
✴ Th⁴⁺: Th = [Rn] 6d² 7s² → Th⁴⁺ = [Rn]

Question 4.2
Why are Mn²⁺ compounds more stable than Fe²⁺ towards oxidation to their +3 state?
Answer
🟦 Mn²⁺ = 3d⁵ (half-filled) → extra stability; oxidation to Mn³⁺ (3d⁴) breaks half-filled symmetry → unfavourable.
🟩 Fe²⁺ = 3d⁶; oxidation to Fe³⁺ (3d⁵) gains half-filled stability → favourable.
📌 Hence Mn²⁺ resists oxidation, Fe²⁺ is readily oxidised to Fe³⁺.

Question 4.3
Explain briefly how +2 state becomes more and more stable in the first half of the first-row transition elements with increasing atomic number.
Answer
🔵 From Sc → Mn the common +2 state arises by loss of 4s² only, leaving (n−1)dⁿ unchanged.
🟢 With increasing nuclear charge, removal of an extra d-electron (to make +3 or higher) becomes progressively harder.
🟠 Therefore, relative stability shifts towards +2 (Ti²⁺ < V²⁺ < Cr²⁺ < Mn²⁺), with Mn²⁺ (d⁵) being most stable due to half-filled shell.

Question 4.4
To what extent do the electronic configurations decide the stability of oxidation states in the first series of transition elements? Illustrate with examples.
Answer
🟦 Highest OS ≈ group number up to Mn: V(+5), Cr(+6), Mn(+7) because (n−1)d and ns electrons are available for bonding.
🟩 d⁵ / d¹⁰ stability modulates trends:
Mn²⁺ (d⁵), Fe³⁺ (d⁵) are specially stable.
Cu⁺ (d¹⁰) is stabilized; Zn²⁺ (d¹⁰) is dominant.
🟨 Later elements (Fe, Co, Ni, Cu) show lower maximum OS (e.g., Fe up to +6, Co up to +3/+4, Ni up to +4, Cu up to +3) due to rising ionisation enthalpy of removing d-electrons.
📌 Thus configuration (half-/fully-filled d) and ns–(n−1)d energy closeness jointly control stability.

Question 4.5
What may be the stable oxidation state of the transition element with the following ground-state d-electron configurations: 3d³, 3d⁵ and 3d⁷?
Answer
🔵 3d³ (like V): total valence e⁻ = d³ + s² → +5 often most stable (vanadates).
🟢 3d⁵ (like Mn): valence = 5 + 2 → +7 most stable (permanganate).
🟠 3d⁷ (like Co): although group number = 9, very high OS is not accessible; +2 and +3 are most stable (Co²⁺, Co³⁺).
📌 Reason: Maximum OS ≈ group number only up to Mn; thereafter it falls because removing more d-electrons becomes difficult.

Question 4.6
Name the oxometal anions of the first-row transition metals in which the metal exhibits oxidation state equal to its group number.
Answer
🟦 V (+5) → vanadate: VO₃⁻ / VO₄³⁻
🟩 Cr (+6) → chromate/dichromate: CrO₄²⁻, Cr₂O₇²⁻
🟨 Mn (+7) → permanganate: MnO₄⁻
(For Ti (+4), titanates such as TiO₃²⁻ exist but the classic equal-group anions emphasized are V, Cr, Mn.)

Question 4.7
What is lanthanoid contraction? What are its consequences?
Answer
🔵 Definition: Steady decrease in ionic/atomic radii of Ln³⁺ (Ce³⁺ → Lu³⁺) due to poor shielding by 4f electrons.
🔶 Consequences:
(i) Zr–Hf and other 4d/5d pairs have almost identical sizes → very similar chemistry → difficult separation.
(ii) Basicity of Ln(OH)₃ decreases from La³⁺ to Lu³⁺.
(iii) Ionic radii shrink across lanthanoids → affects complex stability and colour.

Question 4.8
What are the characteristics of the transition elements and why are they called transition elements? Which d-block elements may not be regarded as transition elements?
Answer
🟦 Key characteristics: variable OS, formation of coloured ions/complexes, paramagnetism, catalytic activity, alloy formation, high enthalpy of atomisation.
🟩 Called “transition”: they form a transition between s- and p-blocks; more precisely, they have partially filled (n−1)d subshell in ground state or common OS.
🟠 Not regarded: Zn, Cd, Hg (Group 12) — d¹⁰ in ground as well as common +2 state; hence lack many transition-metal features.

Question 4.9
In what way is the electronic configuration of the transition elements different from that of the non-transition elements?
Answer
🔵 Transition: general (n−1)d¹–⁹ ns¹–² (partially filled d either in atom or common ion).
🟢 Non-transition: d-subshell either absent (s-/p-block) or completely filled (d¹⁰) in atom and common ions (e.g., Zn²⁺ = d¹⁰).
📌 Result: transition metals show variable OS, coloured ions, paramagnetism—features largely absent in non-transition elements.

Question 4.10
What are the different oxidation states exhibited by the lanthanoids?
Answer
🟦 Predominant: +3 for all lanthanoids.
🟩 Also observed (stabilised by f⁰ / f⁷ / f¹⁴ configurations):
+4: Ce⁴⁺, Pr⁴⁺, Tb⁴⁺ (→ f⁰ / f¹ / f⁷ tendencies).
+2: Sm²⁺, Eu²⁺, Yb²⁺ (→ f⁶, f⁷, f¹⁴).
📌 Others occur rarely and are strongly oxidising/reducing to revert to +3.

Question 4.11
Explain giving reasons:
(i) Transition metals and many of their compounds show paramagnetic behaviour.
(ii) The enthalpies of atomisation of the transition metals are high.
(iii) Transition metals generally form coloured compounds.
(iv) Transition metals and their compounds act as good catalysts.
Answer
🧲 (i) Paramagnetism: presence of unpaired d-electrons ⇒ magnetic moment μ = √(n(n+2)) BM.
🔗 (ii) High atomisation enthalpy: strong metallic bonding due to extensive d–d overlap and participation of multiple valence electrons.
🎨 (iii) Colour: d–d transitions under ligand field; sometimes charge-transfer transitions.
⚗ (iv) Catalysis: variable OS ↔ ease of redox, formation of intermediate complexes, and large surface for adsorption.

Question 4.12
What are interstitial compounds? Why are such compounds well known for transition metals?
Answer
🔵 Definition: Small atoms (H, C, N, B) occupy interstices (voids) in a metal lattice without disturbing its framework → non-stoichiometric phases (e.g., TiC, Fe₃C, VN).
🟢 Why common for TMs:
(i) Close-packed lattices with octa/tetra-voids of suitable size,
(ii) High coordination & metallic bonding tolerate guests,
(iii) Resulting phases are hard, chemically inert, high-melting, yet often conducting.

Question 4.13
How is the variability in oxidation states of transition metals different from that of the non-transition metals? Illustrate with examples.
Answer
🟦 Transition metals: successive OS often differ by 1 due to similar energies of ns and (n−1)d electrons.
Examples: V (+2 to +5), Cr (+2, +3, +6), Mn (+2 to +7), Fe (+2, +3, +6).
🟩 Non-transition p-block: common OS generally differ by 2 (inert-pair effect).
Examples: Sn (+2, +4), Pb (+2, +4), S (−2, +4, +6).
📌 Transition metals thus show greater multiplicity and continuity of oxidation states.

Question 4.14
Describe the preparation of potassium dichromate from iron chromite ore. What is the effect of increasing pH on a solution of potassium dichromate?
Answer
🟦 Preparation steps
Fusion: FeCr₂O₄ + Na₂CO₃ + O₂ → Na₂CrO₄ + Fe₂O₃
Leaching: Na₂CrO₄ (yellow solution) separated from Fe₂O₃.
Acidification: 2CrO₄²⁻ + 2H⁺ ⇌ Cr₂O₇²⁻ + H₂O (orange).
Crystallisation: Addition of KCl → K₂Cr₂O₇ (orange crystals).
🟢 Effect of pH
Acidic medium → dichromate (Cr₂O₇²⁻, orange) stable.
Basic medium → chromate (CrO₄²⁻, yellow) predominates.
📌 Colour change with pH = yellow ⇌ orange.

Question 4.15
Describe the oxidising action of potassium dichromate and write the ionic equations for its reaction with:
(i) I⁻ (ii) Fe²⁺ (iii) H₂S
Answer
🟦 General reaction: Cr₂O₇²⁻ + 14H⁺ + 6e⁻ → 2Cr³⁺ + 7H₂O
(i) With iodide
Cr₂O₇²⁻ + 14H⁺ + 6I⁻ → 2Cr³⁺ + 7H₂O + 3I₂
(ii) With Fe²⁺
Cr₂O₇²⁻ + 14H⁺ + 6Fe²⁺ → 2Cr³⁺ + 7H₂O + 6Fe³⁺
(iii) With H₂S
Cr₂O₇²⁻ + 14H⁺ + 3H₂S → 2Cr³⁺ + 7H₂O + 3S↓
📌 Potassium dichromate acts as a strong oxidising agent in acidic medium.

Question 4.16
Describe the preparation of potassium permanganate. How does the acidified permanganate solution react with:
(i) Fe²⁺ (ii) SO₂ (iii) Oxalic acid? Write the ionic equations.
Answer
🟦 Preparation
Pyrolusite (MnO₂) fused with KOH + O₂ → K₂MnO₄ (green).
Disproportionation in acidic medium: 3MnO₄²⁻ + 4H⁺ → 2MnO₄⁻ + MnO₂ + 2H₂O.
Purple KMnO₄ crystals obtained.
🟢 Reactions in acidic medium (MnO₄⁻ + 8H⁺ + 5e⁻ → Mn²⁺ + 4H₂O)
(i) With Fe²⁺:
MnO₄⁻ + 8H⁺ + 5Fe²⁺ → Mn²⁺ + 5Fe³⁺ + 4H₂O
(ii) With SO₂:
2MnO₄⁻ + 5SO₂ + 2H₂O → 2Mn²⁺ + 5SO₄²⁻ + 4H⁺
(iii) With oxalic acid (C₂O₄²⁻):
2MnO₄⁻ + 16H⁺ + 5C₂O₄²⁻ → 2Mn²⁺ + 10CO₂ + 8H₂O
📌 KMnO₄ is a very strong oxidising agent.

Question 4.17
For M³⁺/M and M³⁺/M²⁺ systems, E° values are:
Cr³⁺/Cr: −0.9 V, Cr³⁺/Cr²⁺: −0.4 V, Mn³⁺/Mn: −1.2 V, Mn³⁺/Mn²⁺: +1.5 V, Fe³⁺/Fe: −0.4 V, Fe³⁺/Fe²⁺: +0.8 V.
Use this data to comment upon:
(i) Stability of Fe³⁺ in acid vs Cr³⁺/Mn³⁺
(ii) Ease of oxidation of Fe vs Cr or Mn
Answer
🟦 (i) Fe³⁺/Fe²⁺ = +0.8 V → Fe³⁺ reduced easily → Fe³⁺ is stable in acid.
Cr³⁺/Cr²⁺ = −0.4 V → Cr³⁺ less easily reduced, less stable.
Mn³⁺/Mn²⁺ = +1.5 V → Mn³⁺ strongly oxidising, unstable in solution.
🟢 (ii) Fe³⁺/Fe = −0.4 V → Fe easier to oxidise than Cr (−0.9) or Mn (−1.2).
📌 Thus Fe oxidises more readily; Mn³⁺ is unstable, Fe³⁺ stable in acid.

Question 4.18
Predict which of the following will be coloured in aqueous solution: Ti³⁺, V³⁺, Cu⁺, Sc³⁺, Mn²⁺, Fe³⁺, Co²⁺.
Answer
💡 Colour arises from d–d transitions (partially filled d-orbitals).
Coloured: Ti³⁺ (d¹), V³⁺ (d²), Mn²⁺ (d⁵), Fe³⁺ (d⁵), Co²⁺ (d⁷)
Colourless: Cu⁺ (d¹⁰), Sc³⁺ (d⁰)
📌 Coloured ions ⇌ presence of partially filled d-orbitals.

Question 4.19
Compare stability of +2 oxidation state for first-series transition elements.
Answer
🟦 Early elements (Sc, Ti, V, Cr): +2 less stable (easily oxidised).
🟩 Middle (Mn, Fe, Co, Ni): +2 quite stable (Mn²⁺, Fe²⁺, Co²⁺, Ni²⁺).
🟨 Cu²⁺ stable but Cu⁺ disproportionates.
📌 Stability rises across period, peaks near Mn–Ni, then declines.

Question 4.20
Compare chemistry of actinoids with lanthanoids.
Answer
🟦 Electronic config: Both involve filling of f-orbitals (4f vs 5f).
🟩 Oxidation states: Lanthanoids mainly +3; actinoids variable (+3 → +6).
🟨 Radioactivity: Lanthanoids mostly stable; actinoids mostly radioactive.
🟧 Reactivity: Actinoids more reactive, especially towards air/water.
🟪 Contraction: Both show contraction (lanthanoid vs actinoid).
📌 Overall, actinoids have richer redox chemistry and radioactivity.

Question 4.21
How would you account for:
(i) Mn³⁺ strongly reducing, Mn²⁺ stable
(ii) Cobalt(III) unstable in aqueous solution
(iii) d⁴ configuration unstable in ions
Answer
(i) Mn²⁺ (d⁵) = half-filled stability ⇒ Mn³⁺ reduces to Mn²⁺.
(ii) Co³⁺ has very high hydration enthalpy but in water reduces to Co²⁺ (more stable).
(iii) d⁴ tends to convert to more stable d³ (Cr³⁺) or d⁵ (Mn²⁺).

Question 4.22
What is meant by disproportionation? Give two examples.
Answer
🔵 Definition: When a species simultaneously undergoes oxidation and reduction.
🧪 Examples:
Cu⁺ → Cu²⁺ + Cu
2MnO₄²⁻ + 2H₂O → MnO₄⁻ + MnO₂ + 4OH⁻
📌 Characteristic of elements showing intermediate oxidation states.

Question 4.23
Which metal in first series of transition metals exhibits +1 OS most frequently and why?
Answer
🟦 Copper → [Ar] 3d¹⁰ 4s¹.
🟩 Loses one 4s electron → Cu⁺ (3d¹⁰) stable due to filled d-subshell.
📌 Hence +1 oxidation state common for Cu.

Question 4.24
Calculate number of unpaired electrons in gaseous Mn³⁺, Cr³⁺, V³⁺, Ti³⁺. Which is most stable in aqueous solution?
Answer
Mn³⁺ (Z=25): [Ar] 3d⁴ → 4 unpaired.
Cr³⁺ (Z=24): [Ar] 3d³ → 3 unpaired.
V³⁺ (Z=23): [Ar] 3d² → 2 unpaired.
Ti³⁺ (Z=22): [Ar] 3d¹ → 1 unpaired.
🟢 Stability: Mn³⁺ unstable (reduces to Mn²⁺, half-filled d⁵ stable).
📌 Most stable: Cr³⁺ (due to t₂g³ half-filled stability in octahedral field).

Question 4.25
Give examples and reasons for:
(i) Lowest oxide of TM basic; highest oxide acidic.
(ii) Highest OS in oxides/fluorides.
(iii) Highest OS in oxoanions.
Answer
(i) MnO (Mn²⁺) → basic; Mn₂O₇ (Mn⁷⁺) → acidic.
(ii) OsO₄, RuO₄, MnF₄, PtF₆ → high OS.
(iii) Mn in MnO₄⁻ (+7), Cr in Cr₂O₇²⁻ (+6).
📌 As OS increases, oxides become more covalent & acidic.

Question 4.26
Indicate steps in preparation of:
(i) K₂Cr₂O₇ from chromite ore
(ii) KMnO₄ from pyrolusite
Answer
(i) Chromite ore → Na₂CrO₄ (fusion) → Cr₂O₇²⁻ (acidification) → K₂Cr₂O₇ (crystallisation).
(ii) Pyrolusite (MnO₂) + KOH + O₂ → K₂MnO₄ (green) → disproportionation → KMnO₄ (purple).

Question 4.27
What are alloys? Name an important alloy containing some lanthanoid metals. Mention its uses.
Answer
🔵 Alloy: A homogeneous mixture of a metal with other metals or non-metals.
🟢 Important lanthanoid alloy: Mischmetal (≈ 95% lanthanoids, mostly Ce + La + Nd, + Fe and traces of other elements).
🟠 Uses:
In lighter flints.
As reducing agent in extraction of metals.
In special steels.

Question 4.28
What are inner transition elements? Decide which atomic numbers among 29, 59, 74, 95, 102, 104 are inner transition elements.
Answer
🔵 Definition: Elements in which last electron enters (n−2)f orbitals → f-block (lanthanoids + actinoids).
🟢 Given atomic numbers:
29 (Cu) → d-block
59 (Pr) → f-block
74 (W) → d-block
95 (Am) → f-block
102 (No) → f-block
104 (Rf) → d-block
📌 Inner transition elements here: 59, 95, 102.

Question 4.29
The chemistry of actinoids is not so smooth as that of lanthanoids. Justify with examples.
Answer
🟦 Lanthanoids: Almost exclusively +3 oxidation state → regular, smooth chemistry.
🟩 Actinoids: Variable oxidation states due to similar energies of 5f, 6d, 7s orbitals.
🟨 Examples:
U: +3, +4, +5, +6
Np: +3 → +7
Pu: +3 → +7
📌 Hence actinoid chemistry is complex and irregular, unlike lanthanoids.

Question 4.30
Which is the last element in the series of the actinoids? Write its electronic configuration. Comment on the possible oxidation state.
Answer
🟦 Last element: Lawrencium (Lr, Z=103)
🟢 Electronic configuration: [Rn] 5f¹⁴ 6d¹ 7s²
🟠 Possible oxidation state: +3 (most stable, like other actinoids).

Question 4.31
Use Hund’s rule to derive the electronic configuration of Ce³⁺. Calculate its magnetic moment using the spin-only formula.
Answer
🔵 Ce (Z=58): [Xe] 4f² 6s²
🟢 Ce³⁺ = [Xe] 4f¹ (removal of 2 × 6s + 1 × 4f).
🟠 One unpaired electron ⇒ n = 1
📌 μ = √(n(n+2)) = √3 = 1.73 BM

Question 4.32
Name lanthanoids that show +4 OS and those that show +2 OS.
Answer
🟦 +4: Ce, Pr, Tb (stabilised by f⁰, f¹, f⁷)
🟩 +2: Sm, Eu, Yb (stabilised by f⁶, f⁷, f¹⁴)

Question 4.33
Compare chemistry of actinoids with lanthanoids on: (i) electronic configuration (ii) oxidation states (iii) chemical reactivity.
Answer
🟦 Electronic config: Lanthanoids → 4f filling; Actinoids → 5f filling.
🟩 Oxidation states: Lanthanoids → almost always +3; Actinoids → variable (+3 to +6/+7).
🟨 Reactivity: Lanthanoids → less reactive; Actinoids → more reactive, radioactive.

Question 4.34
Write electronic configurations of elements with Z = 61, 91, 101, 109.
Answer
🟦 61 (Pm): [Xe] 4f⁵ 6s²
🟩 91 (Pa): [Rn] 5f² 6d¹ 7s²
🟨 101 (Md): [Rn] 5f¹³ 7s²
🟧 109 (Mt): [Rn] 5f¹⁴ 6d⁷ 7s²

Question 4.35
Compare general characteristics of first-series transition metals with second and third series.
Answer
🟦 Electronic config: All → (n−1)d orbitals; heavier series show relativistic effects.
🟩 Oxidation states: Wider range in 4d/5d than 3d.
🟨 Ionisation enthalpies: Increase down series but irregular due to lanthanoid contraction.
🟧 Atomic radii: 4d and 5d elements have almost same radii (lanthanoid contraction).
📌 5d elements are more stable in higher oxidation states.

Question 4.36
Write no. of 3d electrons in hydrated ions: Ti³⁺, V²⁺, Cr³⁺, Mn²⁺, Fe²⁺, Co²⁺, Ni²⁺, Cu²⁺. Indicate splitting in octahedral field.
Answer
Ti³⁺: d¹
V²⁺: d³
Cr³⁺: d³
Mn²⁺: d⁵
Fe²⁺: d⁶
Co²⁺: d⁷
Ni²⁺: d⁸
Cu²⁺: d⁹
🟢 In octahedral field → d splits into t₂g (lower, 3 orbitals) and e_g (higher, 2 orbitals).
📌 Filling depends on ligand strength (CFSE).

Question 4.37
Comment: Elements of first transition series differ from heavier transition series.
Answer
🟦 3d elements: more variety in oxidation states, less stable in high OS.
🟩 4d/5d: higher enthalpies of atomisation, higher melting points.
🟨 5d metals (due to lanthanoid contraction) are closer in radii to 4d metals, thus chemical similarity (Zr–Hf).
🟧 First series show more pronounced paramagnetism and coloured compounds due to smaller crystal field splitting.

Question 4.38
What can be inferred from magnetic moment values of: [Mn(CN)₆]³⁻ = 2.2 BM, [Fe(H₂O)₆]²⁺ = 5.3 BM, [K₂MnCl₆] = 5.9 BM?
Answer
🔵 [Mn(CN)₆]³⁻: μ = 2.2 BM ≈ 1 unpaired e⁻ → low-spin complex (strong field CN⁻).
🟢 [Fe(H₂O)₆]²⁺: μ = 5.3 BM ≈ 4 unpaired e⁻ → high-spin (weak field H₂O).
🟠 [K₂MnCl₆]: μ = 5.9 BM ≈ 5 unpaired e⁻ → high-spin Mn(IV) with weak field Cl⁻.
📌 Magnetic moment values reveal ligand field strength and spin state.

NEET QUESTIONS FROM THIS LESSON

Q1. Among the following, which ion is coloured in aqueous solution?
🔵 (A) Zn²⁺
🟢 (B) Ti³⁺
🟠 (C) Sc³⁺
🔴 (D) Ca²⁺
Answer: (B) Ti³⁺
Year: 2024 | Shift: 1 | Set: Q
Q2. Which element shows maximum number of oxidation states among 3d series?
🔵 (A) Cr
🟢 (B) Mn
🟠 (C) Fe
🔴 (D) Co
Answer: (B) Mn
Year: 2024 | Shift: 2 | Set: R
Q3. The lanthanoid contraction is mainly due to:
🔵 (A) Poor shielding of 4f electrons
🟢 (B) Increase in nuclear charge
🟠 (C) High electronegativity
🔴 (D) Relativistic effect
Answer: (A) Poor shielding of 4f electrons
Year: 2023 | Shift: 1 | Set: P
Q4. Which of the following has the highest magnetic moment?
🔵 (A) Fe²⁺ (d⁶)
🟢 (B) Mn²⁺ (d⁵)
🟠 (C) Co²⁺ (d⁷)
🔴 (D) Ni²⁺ (d⁸)
Answer: (B) Mn²⁺
Year: 2023 | Shift: 2 | Set: S
Q5. Which of the following does not act as a strong oxidising agent?
🔵 (A) KMnO₄
🟢 (B) K₂Cr₂O₇
🟠 (C) TiCl₄
🔴 (D) Ce⁴⁺ salts
Answer: (C) TiCl₄
Year: 2022 | Shift: 1 | Set: M
Q6. In acidic medium, which of the following is a stronger oxidising agent?
🔵 (A) Cr₂O₇²⁻
🟢 (B) MnO₄⁻
🟠 (C) Fe³⁺
🔴 (D) Cu²⁺
Answer: (B) MnO₄⁻
Year: 2022 | Shift: 2 | Set: N
Q7. Which lanthanoid is used in making permanent magnets?
🔵 (A) Ce
🟢 (B) Nd
🟠 (C) La
🔴 (D) Eu
Answer: (B) Nd
Year: 2021 | Shift: 1 | Set: P
Q8. Which among the following is colourless?
🔵 (A) Mn²⁺
🟢 (B) Ti⁴⁺
🟠 (C) Cr³⁺
🔴 (D) Fe²⁺
Answer: (B) Ti⁴⁺
Year: 2021 | Shift: 2 | Set: Q
Q9. The element with highest melting point in 3d series is:
🔵 (A) Cr
🟢 (B) Mn
🟠 (C) Fe
🔴 (D) V
Answer: (A) Cr
Year: 2020 | Shift: 1 | Set: R
Q10. Which oxidation state is most stable for actinides?
🔵 (A) +2
🟢 (B) +3
🟠 (C) +4
🔴 (D) +6
Answer: (B) +3
Year: 2020 | Shift: 2 | Set: S
Q11. Lanthanoid ions mostly exhibit which type of magnetic behaviour?
🔵 (A) Diamagnetic
🟢 (B) Paramagnetic
🟠 (C) Ferromagnetic
🔴 (D) Antiferromagnetic
Answer: (B) Paramagnetic
Year: 2019 | Shift: 1 | Set: M
Q12. The actinide element used in nuclear reactors as fuel is:
🔵 (A) Th
🟢 (B) U
🟠 (C) Pu
🔴 (D) Am
Answer: (B) U
Year: 2019 | Shift: 2 | Set: N
Q13. Which transition element has maximum number of unpaired electrons?
🔵 (A) Fe
🟢 (B) Mn
🟠 (C) Co
🔴 (D) Ni
Answer: (B) Mn
Year: 2018 | Shift: 1 | Set: P
Q14. Lanthanoid contraction leads to:
🔵 (A) Similarity of Zr and Hf properties
🟢 (B) Similarity of Ti and Zr
🟠 (C) Higher ionisation energy of Ce
🔴 (D) Larger size of La³⁺
Answer: (A) Similarity of Zr and Hf properties
Year: 2018 | Shift: 2 | Set: Q
Q15. Which of the following is colourless?
🔵 (A) Cu²⁺
🟢 (B) Sc³⁺
🟠 (C) Ni²⁺
🔴 (D) Cr³⁺
Answer: (B) Sc³⁺
Year: 2017 | Shift: 1 | Set: R
Q16. Which of the following elements is not considered a transition element?
🔵 (A) Zn
🟢 (B) Cr
🟠 (C) Cu
🔴 (D) Fe
Answer: (A) Zn
Year: 2017 | Shift: 2 | Set: S
Q17. The element used in storage batteries among d-block is:
🔵 (A) Zn
🟢 (B) Pb
🟠 (C) Cd
🔴 (D) Fe
Answer: (C) Cd
Year: 2016 | Shift: 1 | Set: P
Q18. Which oxidation state is most stable for Mn?
🔵 (A) +2
🟢 (B) +3
🟠 (C) +4
🔴 (D) +7
Answer: (A) +2
Year: 2016 | Shift: 2 | Set: Q
Q19. In alkaline medium, KMnO₄ gives colour due to:
🔵 (A) Charge transfer transitions
🟢 (B) d–d transitions
🟠 (C) f–f transitions
🔴 (D) Hybridisation
Answer: (A) Charge transfer transitions
Year: 2015 | Shift: 1 | Set: M
Q20. Which element is radioactive among actinides?
🔵 (A) U
🟢 (B) Th
🟠 (C) Ce
🔴 (D) La
Answer: (A) U
Year: 2015 | Shift: 2 | Set: N
Q21. The most common oxidation state of lanthanoids is:
🔵 (A) +2
🟢 (B) +3
🟠 (C) +4
🔴 (D) +5
Answer: (B) +3
Year: 2014 | AIPMT
Q22. Among 3d metals, the element showing maximum catalytic activity is:
🔵 (A) Fe
🟢 (B) Ni
🟠 (C) V
🔴 (D) Cu
Answer: (B) Ni
Year: 2013 | AIPMT
Q23. Which lanthanoid is used in gas mantles?
🔵 (A) La
🟢 (B) Th
🟠 (C) Ce
🔴 (D) Nd
Answer: (C) Ce
Year: 2012 | AIPMT
Q24. Which ion is most stable in aqueous solution?
🔵 (A) Fe²⁺
🟢 (B) Fe³⁺
🟠 (C) Cu²⁺
🔴 (D) Mn³⁺
Answer: (C) Cu²⁺
Year: 2011 | AIPMT
Q25. Which one of the following shows highest oxidation state?
🔵 (A) Mn
🟢 (B) Cr
🟠 (C) Fe
🔴 (D) V
Answer: (A) Mn
Year: 2010 | AIPMT

Q26. Which actinide is artificially prepared and used as a source of α-particles?
🔵 (A) U
🟢 (B) Th
🟠 (C) Pu
🔴 (D) Am
Answer: (C) Pu
Year: 2009 | AIPMT
Q27. Which of the following transition metal ions is colourless in aqueous solution?
🔵 (A) Cu²⁺
🟢 (B) Ti⁴⁺
🟠 (C) Fe²⁺
🔴 (D) Mn²⁺
Answer: (B) Ti⁴⁺
Year: 2008 | AIPMT
Q28. Which oxidation state of uranium is most stable in aqueous medium?
🔵 (A) +2
🟢 (B) +3
🟠 (C) +4
🔴 (D) +6
Answer: (D) +6
Year: 2008 | AIPMT
Q29. The element used in making powerful permanent magnets is:
🔵 (A) Sm
🟢 (B) Nd
🟠 (C) Ce
🔴 (D) La
Answer: (B) Nd
Year: 2007 | AIPMT
Q30. Which of the following ions will show minimum paramagnetism?
🔵 (A) Ti³⁺
🟢 (B) Mn²⁺
🟠 (C) Cu²⁺
🔴 (D) Sc³⁺
Answer: (D) Sc³⁺
Year: 2007 | AIPMT
Q31. Which one is used in making coloured glasses and enamels?
🔵 (A) Cr₂O₃
🟢 (B) MnO₂
🟠 (C) Fe₂O₃
🔴 (D) CuO
Answer: (B) MnO₂
Year: 2006 | AIPMT
Q32. Which lanthanoid is used in lighter flints?
🔵 (A) La
🟢 (B) Ce
🟠 (C) Nd
🔴 (D) Pr
Answer: (B) Ce
Year: 2006 | AIPMT
Q33. The pink colour of KMnO₄ is due to:
🔵 (A) Charge transfer
🟢 (B) d–d transition
🟠 (C) f–f transition
🔴 (D) Magnetic effect
Answer: (A) Charge transfer
Year: 2005 | AIPMT
Q34. Which one of the following pairs is not correctly matched?
🔵 (A) Zr and Hf – similar size
🟢 (B) La and Lu – lanthanoid contraction
🟠 (C) Cr and Mo – different group
🔴 (D) Cu and Ag – coinage metals
Answer: (C) Cr and Mo – different group
Year: 2005 | AIPMT
Q35. Which element of the actinide series is used in atomic bombs?
🔵 (A) U-238
🟢 (B) U-235
🟠 (C) Th-232
🔴 (D) Pa-231
Answer: (B) U-235
Year: 2004 | AIPMT
Q36. Which of the following is not a property of transition metals?
🔵 (A) Variable oxidation states
🟢 (B) Formation of coloured ions
🟠 (C) High ionisation energy
🔴 (D) Catalytic property
Answer: (C) High ionisation energy
Year: 2003 | AIPMT
Q37. Which actinide is used in smoke detectors?
🔵 (A) U
🟢 (B) Th
🟠 (C) Am
🔴 (D) Np
Answer: (C) Am
Year: 2003 | AIPMT
Q38. The element with atomic number 57 is:
🔵 (A) La
🟢 (B) Ce
🟠 (C) Pr
🔴 (D) Nd
Answer: (A) La
Year: 2002 | AIPMT
Q39. Which ion is most stable in aqueous medium?
🔵 (A) Fe²⁺
🟢 (B) Fe³⁺
🟠 (C) Mn³⁺
🔴 (D) Cu⁺
Answer: (B) Fe³⁺
Year: 2002 | AIPMT
Q40. Which of the following shows least tendency for complex formation?
🔵 (A) Cu²⁺
🟢 (B) Zn²⁺
🟠 (C) Fe³⁺
🔴 (D) Ni²⁺
Answer: (B) Zn²⁺
Year: 2001 | AIPMT
Q41. Which of the following is amphoteric?
🔵 (A) ZnO
🟢 (B) Fe₂O₃
🟠 (C) MnO
🔴 (D) CrO
Answer: (A) ZnO
Year: 2001 | AIPMT
Q42. Which oxidation state is most stable for Ce?
🔵 (A) +2
🟢 (B) +3
🟠 (C) +4
🔴 (D) +5
Answer: (B) +3
Year: 2000 | PMT
Q43. Which element among lanthanoids has electronic configuration [Xe]4f¹⁴5d¹6s²?
🔵 (A) Yb
🟢 (B) Lu
🟠 (C) La
🔴 (D) Nd
Answer: (B) Lu
Year: 1999 | PMT
Q44. Which of the following ions has maximum unpaired electrons?
🔵 (A) Cr³⁺
🟢 (B) Fe³⁺
🟠 (C) Mn²⁺
🔴 (D) Ni²⁺
Answer: (C) Mn²⁺
Year: 1999 | PMT
Q45. Which transition element shows both +2 and +3 stable oxidation states?
🔵 (A) Fe
🟢 (B) Cu
🟠 (C) Zn
🔴 (D) Ag
Answer: (A) Fe
Year: 1998 | PMT
Q46. The lanthanoid used in petroleum cracking is:
🔵 (A) Ce
🟢 (B) La
🟠 (C) Nd
🔴 (D) Sm
Answer: (A) Ce
Year: 1998 | PMT
Q47. The actinide that does not occur naturally is:
🔵 (A) Th
🟢 (B) Pa
🟠 (C) U
🔴 (D) Pu
Answer: (D) Pu
Year: 1997 | PMT
Q48. Which pair of elements are called “actinide twins”?
🔵 (A) U and Pu
🟢 (B) Th and U
🟠 (C) Np and Pu
🔴 (D) Am and Cm
Answer: (A) U and Pu
Year: 1997 | PMT
Q49. Which lanthanoid has electronic configuration [Xe]4f⁷6s²?
🔵 (A) Eu
🟢 (B) Gd
🟠 (C) Tb
🔴 (D) Sm
Answer: (A) Eu
Year: 1996 | PMT
Q50. Which actinide is most stable in +4 oxidation state?
🔵 (A) U
🟢 (B) Th
🟠 (C) Pu
🔴 (D) Np
Answer: (B) Th
Year: 1995 | PMT

JEE MAINS QUESTIONS FROM THIS LESSON

Q1. The oxidation state of Mn in MnO₄⁻ is:
🔵 (A) +6
🟢 (B) +7
🟠 (C) +4
🔴 (D) +5
Answer: (B) +7
Year: 2024 | Shift: 2 | Set: B
Q2. Among the following, the ion with the highest number of unpaired electrons is:
🔵 (A) Fe³⁺
🟢 (B) Mn²⁺
🟠 (C) Cu²⁺
🔴 (D) Ni²⁺
Answer: (B) Mn²⁺
Year: 2024 | Shift: 1 | Set: A
Q3. The actinide used in nuclear power generation as fuel is:
🔵 (A) Th
🟢 (B) U
🟠 (C) Np
🔴 (D) Cm
Answer: (B) U
Year: 2023 | Shift: 2 | Set: C
Q4. Which element shows maximum oxidation states among 3d series?
🔵 (A) Cr
🟢 (B) Mn
🟠 (C) Fe
🔴 (D) Co
Answer: (B) Mn
Year: 2023 | Shift: 1 | Set: D
Q5. The property responsible for similarity between Zr and Hf is:
🔵 (A) Actinide contraction
🟢 (B) Lanthanoid contraction
🟠 (C) Diagonal relationship
🔴 (D) Relativistic effect
Answer: (B) Lanthanoid contraction
Year: 2022 | Shift: 2 | Set: A
Q6. Which transition metal ion is colourless?
🔵 (A) Sc³⁺
🟢 (B) Fe²⁺
🟠 (C) Cu²⁺
🔴 (D) Co²⁺
Answer: (A) Sc³⁺
Year: 2022 | Shift: 1 | Set: C
Q7. Which is a good oxidising agent in acidic medium?
🔵 (A) Cr³⁺
🟢 (B) MnO₄⁻
🟠 (C) Fe²⁺
🔴 (D) Co²⁺
Answer: (B) MnO₄⁻
Year: 2021 | Shift: 2 | Set: A
Q8. The element used in permanent magnets among lanthanoids is:
🔵 (A) La
🟢 (B) Nd
🟠 (C) Ce
🔴 (D) Eu
Answer: (B) Nd
Year: 2021 | Shift: 1 | Set: B
Q9. Which oxidation state of uranium is most stable?
🔵 (A) +3
🟢 (B) +4
🟠 (C) +5
🔴 (D) +6
Answer: (D) +6
Year: 2020 | Shift: 2 | Set: A
Q10. Which ion among the following has maximum paramagnetism?
🔵 (A) Ti³⁺
🟢 (B) Mn²⁺
🟠 (C) Fe³⁺
🔴 (D) Co²⁺
Answer: (B) Mn²⁺
Year: 2020 | Shift: 1 | Set: C
Q11. The compound responsible for purple colour of KMnO₄ is due to:
🔵 (A) f–f transitions
🟢 (B) d–d transitions
🟠 (C) Charge transfer
🔴 (D) Lattice effect
Answer: (C) Charge transfer
Year: 2019 | Shift: 2 | Set: A
Q12. The most common oxidation state of lanthanoids is:
🔵 (A) +2
🟢 (B) +3
🟠 (C) +4
🔴 (D) +5
Answer: (B) +3
Year: 2019 | Shift: 1 | Set: B
Q13. Which among the following does not form coloured ion?
🔵 (A) Zn²⁺
🟢 (B) Cu²⁺
🟠 (C) Cr³⁺
🔴 (D) Ni²⁺
Answer: (A) Zn²⁺
Year: 2018 | Shift: 2 | Set: C
Q14. The lanthanoid contraction is responsible for:
🔵 (A) Similarity of Ti and Zr
🟢 (B) Similarity of Zr and Hf
🟠 (C) Larger ionic radius of Ce
🔴 (D) Higher oxidation states of La
Answer: (B) Similarity of Zr and Hf
Year: 2018 | Shift: 1 | Set: A
Q15. The transition element that shows maximum catalytic property is:
🔵 (A) Cu
🟢 (B) Fe
🟠 (C) Ni
🔴 (D) V
Answer: (C) Ni
Year: 2017 | Shift: 2 | Set: B
Q16. Which oxidation state is most stable for Mn?
🔵 (A) +2
🟢 (B) +3
🟠 (C) +4
🔴 (D) +7
Answer: (A) +2
Year: 2017 | Shift: 1 | Set: D
Q17. Which lanthanoid is used in making gas mantles?
🔵 (A) La
🟢 (B) Ce
🟠 (C) Nd
🔴 (D) Pr
Answer: (B) Ce
Year: 2016 | Shift: 2 | Set: A
Q18. Which ion among the following is most stable in aqueous medium?
🔵 (A) Fe²⁺
🟢 (B) Cu²⁺
🟠 (C) Mn³⁺
🔴 (D) Co³⁺
Answer: (B) Cu²⁺
Year: 2016 | Shift: 1 | Set: B
Q19. The actinide element used in smoke detectors is:
🔵 (A) U
🟢 (B) Th
🟠 (C) Am
🔴 (D) Np
Answer: (C) Am
Year: 2015 | Shift: 2 | Set: A
Q20. Which transition metal oxide is amphoteric?
🔵 (A) ZnO
🟢 (B) MnO₂
🟠 (C) Fe₂O₃
🔴 (D) CrO
Answer: (A) ZnO
Year: 2015 | Shift: 1 | Set: B
Q21. The stable oxidation state of cerium is:
🔵 (A) +2
🟢 (B) +3
🟠 (C) +4
🔴 (D) +5
Answer: (B) +3
Year: 2014 | AIEEE
Q22. Which transition metal ion shows minimum paramagnetism?
🔵 (A) Sc³⁺
🟢 (B) Ti³⁺
🟠 (C) V²⁺
🔴 (D) Mn²⁺
Answer: (A) Sc³⁺
Year: 2013 | AIEEE
Q23. Which ion is colourless?
🔵 (A) Fe²⁺
🟢 (B) Ti⁴⁺
🟠 (C) Mn²⁺
🔴 (D) Co²⁺
Answer: (B) Ti⁴⁺
Year: 2013 | AIEEE
Q24. Which pair is called coinage metals?
🔵 (A) Fe, Co
🟢 (B) Cu, Ag
🟠 (C) Ni, Pd
🔴 (D) Ti, Zr
Answer: (B) Cu, Ag
Year: 2012 | AIEEE
Q25. The actinide showing maximum number of oxidation states is:
🔵 (A) U
🟢 (B) Th
🟠 (C) Np
🔴 (D) Pu
Answer: (C) Np
Year: 2012 | AIEEE

Q26. Which transition element shows both +2 and +3 stable oxidation states?
🔵 (A) Fe
🟢 (B) Cu
🟠 (C) Zn
🔴 (D) Ag
Answer: (A) Fe
Year: 2011 | AIEEE
Q27. Which lanthanoid is used in lighter flints?
🔵 (A) La
🟢 (B) Ce
🟠 (C) Nd
🔴 (D) Sm
Answer: (B) Ce
Year: 2011 | AIEEE
Q28. The ion which is least stable in aqueous medium is:
🔵 (A) Fe²⁺
🟢 (B) Cu²⁺
🟠 (C) Mn³⁺
🔴 (D) Co²⁺
Answer: (C) Mn³⁺
Year: 2010 | AIEEE
Q29. Which transition element is used in electroplating due to its resistance to corrosion?
🔵 (A) Ni
🟢 (B) Cr
🟠 (C) Cu
🔴 (D) Zn
Answer: (B) Cr
Year: 2010 | AIEEE
Q30. Which property is least characteristic of transition elements?
🔵 (A) High melting point
🟢 (B) Multiple oxidation states
🟠 (C) Formation of coloured ions
🔴 (D) Low density
Answer: (D) Low density
Year: 2009 | AIEEE
Q31. The actinide most stable in +4 oxidation state is:
🔵 (A) U
🟢 (B) Th
🟠 (C) Pu
🔴 (D) Np
Answer: (B) Th
Year: 2009 | AIEEE
Q32. Which of the following is diamagnetic?
🔵 (A) Zn²⁺
🟢 (B) Cu²⁺
🟠 (C) Ti³⁺
🔴 (D) Cr³⁺
Answer: (A) Zn²⁺
Year: 2008 | AIEEE
Q33. Which actinide is used in atomic reactors?
🔵 (A) Th-232
🟢 (B) Pa-231
🟠 (C) U-235
🔴 (D) Pu-239
Answer: (C) U-235
Year: 2008 | AIEEE
Q34. Which ion is colourless?
🔵 (A) Ti³⁺
🟢 (B) Ti⁴⁺
🟠 (C) Cr³⁺
🔴 (D) Mn²⁺
Answer: (B) Ti⁴⁺
Year: 2007 | AIEEE
Q35. Which element among lanthanoids has [Xe]4f¹⁴5d¹6s² configuration?
🔵 (A) Yb
🟢 (B) Lu
🟠 (C) Ce
🔴 (D) La
Answer: (B) Lu
Year: 2007 | AIEEE
Q36. Which among the following is paramagnetic?
🔵 (A) Zn²⁺
🟢 (B) Cu⁺
🟠 (C) Cu²⁺
🔴 (D) Sc³⁺
Answer: (C) Cu²⁺
Year: 2006 | AIEEE
Q37. The common oxidation state of actinides is:
🔵 (A) +2
🟢 (B) +3
🟠 (C) +4
🔴 (D) +5
Answer: (B) +3
Year: 2006 | AIEEE
Q38. Which transition element has highest melting point?
🔵 (A) W
🟢 (B) Cr
🟠 (C) Mn
🔴 (D) V
Answer: (A) W
Year: 2005 | AIEEE
Q39. The lanthanoid showing +4 oxidation state most readily is:
🔵 (A) Ce
🟢 (B) Eu
🟠 (C) Yb
🔴 (D) Nd
Answer: (A) Ce
Year: 2005 | AIEEE
Q40. The element used in storage batteries is:
🔵 (A) Zn
🟢 (B) Pb
🟠 (C) Cd
🔴 (D) Ni
Answer: (C) Cd
Year: 2004 | AIEEE
Q41. The ion with configuration [Ar]3d⁵ is:
🔵 (A) Fe²⁺
🟢 (B) Cr³⁺
🟠 (C) Mn²⁺
🔴 (D) Ni²⁺
Answer: (C) Mn²⁺
Year: 2004 | AIEEE
Q42. Which one is called “coinage metal”?
🔵 (A) Ag
🟢 (B) Al
🟠 (C) Mg
🔴 (D) Na
Answer: (A) Ag
Year: 2003 | AIEEE
Q43. The lanthanoid showing electronic configuration [Xe]4f⁷6s² is:
🔵 (A) Eu
🟢 (B) Gd
🟠 (C) Tb
🔴 (D) Sm
Answer: (A) Eu
Year: 2003 | AIEEE
Q44. Which of the following ions is coloured?
🔵 (A) Zn²⁺
🟢 (B) Ti⁴⁺
🟠 (C) Fe²⁺
🔴 (D) Ca²⁺
Answer: (C) Fe²⁺
Year: 2002 | AIEEE
Q45. The element of actinide series used in smoke detectors is:
🔵 (A) Th
🟢 (B) U
🟠 (C) Am
🔴 (D) Pu
Answer: (C) Am
Year: 2002 | AIEEE
Q46. Which transition metal is least reactive and used in jewellery?
🔵 (A) Ni
🟢 (B) Cu
🟠 (C) Ag
🔴 (D) Au
Answer: (D) Au
Year: 2001 | AIEEE
Q47. Which property is common in d-block metals?
🔵 (A) They are soft metals
🟢 (B) They show variable oxidation states
🟠 (C) They have low melting points
🔴 (D) They are poor conductors
Answer: (B) They show variable oxidation states
Year: 2001 | AIEEE
Q48. Which among the following is a radioactive element?
🔵 (A) La
🟢 (B) Ce
🟠 (C) Th
🔴 (D) Yb
Answer: (C) Th
Year: 2000 | PMT
Q49. Which lanthanoid is most abundant?
🔵 (A) La
🟢 (B) Nd
🟠 (C) Ce
🔴 (D) Sm
Answer: (C) Ce
Year: 1999 | PMT
Q50. Which actinide has maximum oxidation states?
🔵 (A) U
🟢 (B) Pu
🟠 (C) Np
🔴 (D) Th
Answer: (B) Pu
Year: 1998 | PMT

JEE ADVANCED QUESTIONS FROM THIS LESSON

🔵 Question 1:
Which of the following ions shows the maximum number of unpaired electrons?
🔴 ① Fe²⁺
🟢 ② Mn²⁺
🟡 ③ Cr³⁺
🔵 ④ Ni²⁺
🟢 Answer: ② Mn²⁺
📘 Exam: JEE Advanced 2013 | Paper 1 | IIT Delhi

🔵 Question 2:
Among the following, the colourless compound is —
🔴 ① Ti³⁺
🟢 ② Sc³⁺
🟡 ③ V³⁺
🔵 ④ Cu²⁺
🟢 Answer: ② Sc³⁺
📘 Exam: JEE Advanced 2012 | Paper 1 | IIT Delhi

🔵 Question 3:
Which transition metal ion is most likely to be stable in an aqueous solution?
🔴 ① Mn³⁺
🟢 ② Fe³⁺
🟡 ③ Cu²⁺
🔵 ④ V²⁺
🟢 Answer: ③ Cu²⁺
📘 Exam: JEE Advanced 2015 | Paper 1 | IIT Bombay

🔵 Question 4:
Which of the following elements has the highest oxidation state?
🔴 ① Mn
🟢 ② Cr
🟡 ③ Fe
🔵 ④ Co
🟢 Answer: ① Mn (+7)
📘 Exam: JEE Advanced 2016 | Paper 1 | IIT Guwahati

🔵 Question 5:
KMnO₄ acts as an oxidising agent in acidic medium because —
🔴 ① Mn⁷⁺ is reduced to Mn²⁺
🟢 ② Mn⁷⁺ is oxidised to Mn⁸⁺
🟡 ③ Mn⁷⁺ forms MnO₂
🔵 ④ Mn⁷⁺ forms Mn³⁺
🟢 Answer: ① Mn⁷⁺ → Mn²⁺
📘 Exam: JEE Advanced 2014 | Paper 1 | IIT Kharagpur

🔵 Question 6:
The lanthanoid contraction is responsible for —
🔴 ① Similar radii of Zr and Hf
🟢 ② Decrease in basic strength of hydroxides from La to Lu
🟡 ③ Irregular electronic configurations
🔵 ④ High oxidation states in actinoids
🟢 Answer: ① Similar radii of Zr and Hf
📘 Exam: JEE Advanced 2017 | Paper 1 | IIT Madras

🔵 Question 7:
Which of the following pairs has nearly the same atomic radii?
🔴 ① Zr and Hf
🟢 ② Nb and Ta
🟡 ③ Ti and Zr
🔵 ④ Mo and W
🟢 Answer: ① Zr and Hf
📘 Exam: JEE Advanced 2011 | Paper 1 | IIT Kanpur

🔵 Question 8:
Which of the following oxides is amphoteric?
🔴 ① CrO₃
🟢 ② Cr₂O₃
🟡 ③ Mn₂O₇
🔵 ④ MnO₂
🟢 Answer: ② Cr₂O₃
📘 Exam: JEE Advanced 2013 | Paper 1 | IIT Delhi

🔵 Question 9:
Which of the following shows variable oxidation states?
🔴 ① Ca
🟢 ② Ti
🟡 ③ Zn
🔵 ④ Mg
🟢 Answer: ② Ti
📘 Exam: JEE Advanced 2014 | Paper 1 | IIT Kharagpur

🔵 Question 10:
In the complex [Fe(CN)₆]³⁻, the magnetic moment (in B.M.) is approximately —
🔴 ① 5.9
🟢 ② 1.73
🟡 ③ 0
🔵 ④ 2.83
🟢 Answer: ② 1.73 (B.M.)
📘 Exam: JEE Advanced 2016 | Paper 1 | IIT Guwahati

🔵 Question 11:
Which one of the following has the maximum number of oxidation states?
🔴 ① Mn
🟢 ② Fe
🟡 ③ Cr
🔵 ④ V
🟢 Answer: ① Mn
📘 Exam: JEE Advanced 2012 | Paper 1 | IIT Delhi

🔵 Question 12:
Among the following species, the one having the smallest ionic radius is —
🔴 ① Fe²⁺
🟢 ② Fe³⁺
🟡 ③ Mn²⁺
🔵 ④ Cr²⁺
🟢 Answer: ② Fe³⁺
📘 Exam: JEE Advanced 2015 | Paper 1 | IIT Bombay

🔵 Question 13:
Which statement about actinoids is incorrect?
🔴 ① They are all radioactive.
🟢 ② They show more oxidation states than lanthanoids.
🟡 ③ Actinoids are less reactive than lanthanoids.
🔵 ④ Actinoids have larger ionic radii than lanthanoids.
🟢 Answer: ③ Actinoids are less reactive than lanthanoids. (Incorrect)
📘 Exam: JEE Advanced 2017 | Paper 1 | IIT Madras

🔵 Question 14:
Which of the following has the highest spin-only magnetic moment?
🔴 ① Fe²⁺
🟢 ② Mn²⁺
🟡 ③ Cr³⁺
🔵 ④ Ni²⁺
🟢 Answer: ② Mn²⁺ (5 unpaired electrons)
📘 Exam: JEE Advanced 2014 | Paper 1 | IIT Kharagpur

🔵 Question 15:
Which of the following is a reducing agent in acidic medium?
🔴 ① MnO₂
🟢 ② Cr²⁺
🟡 ③ Cr₂O₇²⁻
🔵 ④ MnO₄⁻
🟢 Answer: ② Cr²⁺
📘 Exam: JEE Advanced 2018 | Paper 1 | IIT Kanpur

🔵 Question 16:
When KMnO₄ acts as an oxidising agent in alkaline medium, the oxidation state of Mn changes from —
🔴 ① +7 to +2
🟢 ② +7 to +4
🟡 ③ +6 to +2
🔵 ④ +4 to +2
🟢 Answer: ② +7 to +4
📘 Exam: JEE Advanced 2015 | Paper 1 | IIT Bombay

🔵 Question 17:
Which one of the following statements is true for transition elements?
🔴 ① They always form colourless ions.
🟢 ② They often exhibit variable oxidation states.
🟡 ③ They have no catalytic properties.
🔵 ④ They form only ionic compounds.
🟢 Answer: ② They often exhibit variable oxidation states.
📘 Exam: JEE Advanced 2019 | Paper 1 | IIT Roorkee

🔵 Question 18:
Which of the following oxides of manganese is most stable?
🔴 ① MnO
🟢 ② Mn₂O₃
🟡 ③ MnO₂
🔵 ④ Mn₂O₇
🟢 Answer: ③ MnO₂
📘 Exam: JEE Advanced 2011 | Paper 1 | IIT Kanpur

🔵 Question 19:
Which pair of ions exhibits the same number of unpaired electrons?
🔴 ① Fe²⁺ and Mn²⁺
🟢 ② Ti³⁺ and V⁴⁺
🟡 ③ Cr³⁺ and Fe³⁺
🔵 ④ Co²⁺ and Ni²⁺
🟢 Answer: ② Ti³⁺ and V⁴⁺ (both have 1 unpaired electron)
📘 Exam: JEE Advanced 2014 | Paper 1 | IIT Kharagpur

🔵 Question 20:
Which of the following pairs represents lanthanoid contraction correctly?
🔴 ① Ce → Lu, decrease in atomic radius
🟢 ② La → Ce, increase in radius
🟡 ③ Zr → Hf, increase in radius
🔵 ④ Ce → La, decrease in radius
🟢 Answer: ① Ce → Lu, decrease in atomic radius
📘 Exam: JEE Advanced 2015 | Paper 1 | IIT Bombay

🔵 Question 21:
Which of the following ions will have the highest magnetic moment?
🔴 ① Cr³⁺
🟢 ② Fe³⁺
🟡 ③ Mn²⁺
🔵 ④ Co²⁺
🟢 Answer: ③ Mn²⁺ (5 unpaired electrons → 5.92 B.M.)
📘 Exam: JEE Advanced 2016 | Paper 1 | IIT Guwahati

🔵 Question 22:
Which among the following is not a transition element?
🔴 ① Zn
🟢 ② Fe
🟡 ③ Ni
🔵 ④ Cr
🟢 Answer: ① Zn (completely filled d¹⁰ configuration)
📘 Exam: JEE Advanced 2013 | Paper 1 | IIT Delhi

🔵 Question 23:
Which among the following elements exhibits +7 oxidation state?
🔴 ① Mn
🟢 ② Cr
🟡 ③ Fe
🔵 ④ Co
🟢 Answer: ① Mn
📘 Exam: JEE Advanced 2012 | Paper 1 | IIT Delhi

🔵 Question 24:
The compound K₂Cr₂O₇ in acidic medium acts as —
🔴 ① Reducing agent
🟢 ② Oxidising agent
🟡 ③ Catalyst
🔵 ④ Precipitating agent
🟢 Answer: ② Oxidising agent
📘 Exam: JEE Advanced 2018 | Paper 1 | IIT Kanpur

🔵 Question 25:
Which of the following transition metal ions has a d⁵ configuration and is stable in both +2 and +3 oxidation states?
🔴 ① Fe
🟢 ② Mn
🟡 ③ Co
🔵 ④ Cr
🟢 Answer: ① Fe (Fe²⁺ → 3d⁶, Fe³⁺ → 3d⁵)
📘 Exam: JEE Advanced 2014 | Paper 1 | IIT Kharagpur

🔵 Question 26:
Which of the following pairs shows the same oxidation state for both elements?
🔴 ① Fe₂O₃ and Cr₂O₃
🟢 ② MnO₂ and Fe₂O₃
🟡 ③ CrO₃ and FeO
🔵 ④ Cr₂O₇²⁻ and MnO₂
🟢 Answer: ① Fe₂O₃ and Cr₂O₃ (both +3)
📘 Exam: JEE Advanced 2017 | Paper 1 | IIT Madras

🔵 Question 27:
The actinoids exhibit larger number of oxidation states than lanthanoids because —
🔴 ① 5f, 6d, and 7s levels are of comparable energies
🟢 ② 4f, 5d, and 6s levels are of comparable energies
🟡 ③ 6f, 7d, and 8s levels are of comparable energies
🔵 ④ They have smaller size
🟢 Answer: ① 5f, 6d, and 7s levels are of comparable energies
📘 Exam: JEE Advanced 2015 | Paper 1 | IIT Bombay

🔵 Question 28:
Which of the following ions is colourless in aqueous solution?
🔴 ① Mn²⁺
🟢 ② Ti⁴⁺
🟡 ③ Cr³⁺
🔵 ④ Cu²⁺
🟢 Answer: ② Ti⁴⁺ (no unpaired d electrons)
📘 Exam: JEE Advanced 2013 | Paper 1 | IIT Delhi

🔵 Question 29:
Among the following, the strongest oxidising agent is —
🔴 ① MnO₂
🟢 ② KMnO₄
🟡 ③ CrO₃
🔵 ④ Cr₂O₇²⁻
🟢 Answer: ② KMnO₄
📘 Exam: JEE Advanced 2016 | Paper 1 | IIT Guwahati

🔵 Question 30:
Which of the following is a d-block element but not a transition element?
🔴 ① Zn
🟢 ② Cu
🟡 ③ Fe
🔵 ④ Ti
🟢 Answer: ① Zn
📘 Exam: JEE Advanced 2011 | Paper 1 | IIT Kanpur

🔵 Question 31:
Which of the following elements shows both +2 and +3 oxidation states and forms coloured compounds in both states?
🔴 ① Mn
🟢 ② Cr
🟡 ③ Fe
🔵 ④ Co
🟢 Answer: ③ Fe (Fe²⁺ & Fe³⁺ both coloured)
📘 Exam: JEE Advanced 2019 | Paper 1 | IIT Roorkee

🔵 Question 32:
Among the following, which element exhibits the highest magnetic moment?
🔴 ① Cr³⁺
🟢 ② Mn²⁺
🟡 ③ Fe³⁺
🔵 ④ Co²⁺
🟢 Answer: ② Mn²⁺ (5 unpaired electrons)
📘 Exam: JEE Advanced 2020 | Paper 1 | IIT Delhi

🔵 Question 33:
Which of the following statements about lanthanoids is correct?
🔴 ① They show limited oxidation states (+2, +3, +4).
🟢 ② They are known for high magnetic moments.
🟡 ③ They form complex ions easily.
🔵 ④ All are non-radioactive.
🟢 Answer: ① They show limited oxidation states (+2, +3, +4).
📘 Exam: JEE Advanced 2018 | Paper 1 | IIT Kanpur

🔵 Question 34:
Which of the following is correct about actinoids compared to lanthanoids?
🔴 ① Actinoids are less reactive.
🟢 ② Actinoids exhibit greater range of oxidation states.
🟡 ③ Actinoids have no radioactive members.
🔵 ④ Actinoids show no contraction.
🟢 Answer: ② Actinoids exhibit greater range of oxidation states.
📘 Exam: JEE Advanced 2017 | Paper 1 | IIT Madras

PRACTICE SETS FROM THIS LESSON

🔹 NEET Level (Q1–Q20)
Q1. Which of the following is not a transition element?
🔵 (A) Fe
🟢 (B) Zn
🟠 (C) Cr
🔴 (D) Ni
Answer: (B) Zn
Q2. The common oxidation state for lanthanoids is:
🔵 (A) +2
🟢 (B) +3
🟠 (C) +4
🔴 (D) +5
Answer: (B) +3
Q3. The ion with a half-filled d-subshell is:
🔵 (A) Mn²⁺
🟢 (B) Fe²⁺
🟠 (C) Cr²⁺
🔴 (D) Co²⁺
Answer: (A) Mn²⁺
Q4. The purple colour of KMnO₄ is due to:
🔵 (A) d–d transition
🟢 (B) f–f transition
🟠 (C) Charge transfer
🔴 (D) Ionisation
Answer: (C) Charge transfer
Q5. Which of the following is colourless in solution?
🔵 (A) Ti³⁺
🟢 (B) V³⁺
🟠 (C) Zn²⁺
🔴 (D) Mn²⁺
Answer: (C) Zn²⁺
Q6. Which element shows maximum number of oxidation states?
🔵 (A) Cr
🟢 (B) Mn
🟠 (C) Fe
🔴 (D) Co
Answer: (B) Mn
Q7. The ion stable due to fully filled d-subshell is:
🔵 (A) Cu²⁺
🟢 (B) Zn²⁺
🟠 (C) Ni²⁺
🔴 (D) Co²⁺
Answer: (B) Zn²⁺
Q8. The alloy mischmetal is used in:
🔵 (A) Fertilisers
🟢 (B) Lighter flints
🟠 (C) Steel reinforcement
🔴 (D) Catalysis
Answer: (B) Lighter flints
Q9. Which is the last actinoid?
🔵 (A) No
🟢 (B) Lr
🟠 (C) Md
🔴 (D) Es
Answer: (B) Lr
Q10. The cause of lanthanoid contraction is:
🔵 (A) Poor shielding of 3d electrons
🟢 (B) Poor shielding of 4f electrons
🟠 (C) Poor shielding of 5d electrons
🔴 (D) Poor shielding of 6d electrons
Answer: (B) Poor shielding of 4f electrons
Q11. Which transition metal is used in the Contact process?
🔵 (A) V
🟢 (B) Mn
🟠 (C) Fe
🔴 (D) Ni
Answer: (A) V
Q12. The ion with maximum paramagnetism:
🔵 (A) Fe²⁺
🟢 (B) Mn²⁺
🟠 (C) Co²⁺
🔴 (D) Ni²⁺
Answer: (B) Mn²⁺
Q13. Which compound is a strong oxidising agent in acidic medium?
🔵 (A) KMnO₄
🟢 (B) K₂MnO₄
🟠 (C) FeCl₂
🔴 (D) CuSO₄
Answer: (A) KMnO₄
Q14. Which ion is colourless:
🔵 (A) La³⁺
🟢 (B) Ce³⁺
🟠 (C) Nd³⁺
🔴 (D) Tb³⁺
Answer: (A) La³⁺
Q15. The stable oxidation state of Cu is:
🔵 (A) +1
🟢 (B) +2
🟠 (C) +3
🔴 (D) +4
Answer: (A) +1
Q16. Which shows disproportionation?
🔵 (A) Cu⁺
🟢 (B) Fe²⁺
🟠 (C) Mn²⁺
🔴 (D) Ni²⁺
Answer: (A) Cu⁺
Q17. Which of the following shows variable oxidation states?
🔵 (A) Ca
🟢 (B) Sc
🟠 (C) Fe
🔴 (D) Na
Answer: (C) Fe
Q18. Which is not a property of transition metals?
🔵 (A) Variable oxidation states
🟢 (B) Colourless ions
🟠 (C) Catalytic activity
🔴 (D) Alloy formation
Answer: (B) Colourless ions
Q19. Which element belongs to Group 12?
🔵 (A) Zn
🟢 (B) Fe
🟠 (C) Cu
🔴 (D) Ni
Answer: (A) Zn
Q20. The half-filled stability is observed in:
🔵 (A) Fe³⁺
🟢 (B) Mn²⁺
🟠 (C) Cr³⁺
🔴 (D) All of these
Answer: (D) All of these

🔹 JEE Main Level (Q21–Q40)
Q21. Which of the following has the highest magnetic moment?
🔵 (A) Fe²⁺ (d⁶)
🟢 (B) Mn²⁺ (d⁵)
🟠 (C) Ni²⁺ (d⁸)
🔴 (D) Co²⁺ (d⁷)
Answer: (B) Mn²⁺
Q22. The E° value of Mn³⁺/Mn²⁺ is +1.5 V. This means:
🔵 (A) Mn³⁺ is unstable in solution
🟢 (B) Mn²⁺ is unstable in solution
🟠 (C) Both are equally stable
🔴 (D) Mn³⁺ easily reduces to Mn²⁺
Answer: (D) Mn³⁺ easily reduces to Mn²⁺
Q23. Which of the following oxides is amphoteric?
🔵 (A) MnO
🟢 (B) Cr₂O₃
🟠 (C) ZnO
🔴 (D) Fe₂O₃
Answer: (B) Cr₂O₃
Q24. Which of the following complexes will be colourless?
🔵 (A) [Ti(H₂O)₆]³⁺
🟢 (B) [Sc(H₂O)₆]³⁺
🟠 (C) [Cr(H₂O)₆]³⁺
🔴 (D) [Fe(H₂O)₆]²⁺
Answer: (B) [Sc(H₂O)₆]³⁺
Q25. Which of the following statements is true for actinoids but not for lanthanoids?
🔵 (A) Show +3 state predominantly
🟢 (B) Exhibit greater range of oxidation states
🟠 (C) Show contraction in size
🔴 (D) Form coloured ions
Answer: (B) Exhibit greater range of oxidation states
Q26. Which of the following is used in making permanent magnets?
🔵 (A) Mischmetal
🟢 (B) Nd–Fe–B alloy
🟠 (C) Bronze
🔴 (D) Brass
Answer: (B) Nd–Fe–B alloy
Q27. Which is the most stable oxidation state of uranium?
🔵 (A) +2
🟢 (B) +3
🟠 (C) +4
🔴 (D) +6
Answer: (D) +6
Q28. The lanthanoid contraction causes:
🔵 (A) Decrease in basicity of hydroxides
🟢 (B) Similarity of Zr and Hf
🟠 (C) Difficulty in separation of lanthanoids
🔴 (D) All of these
Answer: (D) All of these
Q29. Which property decreases across lanthanoid series?
🔵 (A) Atomic number
🟢 (B) Ionic radii
🟠 (C) Nuclear charge
🔴 (D) Electronegativity
Answer: (B) Ionic radii
Q30. Which ion is most stable due to f⁷ configuration?
🔵 (A) Eu²⁺
🟢 (B) Sm²⁺
🟠 (C) Tb⁴⁺
🔴 (D) Ce⁴⁺
Answer: (A) Eu²⁺
Q31. Which ion shows maximum tendency to form complexes?
🔵 (A) Zn²⁺
🟢 (B) Cu²⁺
🟠 (C) Mn²⁺
🔴 (D) Ni²⁺
Answer: (B) Cu²⁺
Q32. Which is the oxidation state of Mn in K₂MnO₄?
🔵 (A) +4
🟢 (B) +5
🟠 (C) +6
🔴 (D) +7
Answer: (C) +6
Q33. Which is not true for transition metals?
🔵 (A) High melting points
🟢 (B) High enthalpy of atomisation
🟠 (C) Only one oxidation state
🔴 (D) Good catalysts
Answer: (C) Only one oxidation state
Q34. Which of the following is an actinoid?
🔵 (A) Gd
🟢 (B) Tb
🟠 (C) Th
🔴 (D) Yb
Answer: (C) Th
Q35. In which series do elements have similar atomic radii due to lanthanoid contraction?
🔵 (A) 3d and 4d
🟢 (B) 4d and 5d
🟠 (C) 5d and 6d
🔴 (D) 2d and 3d
Answer: (B) 4d and 5d
Q36. The stable oxidation state of Ce is:
🔵 (A) +2
🟢 (B) +3
🟠 (C) +4
🔴 (D) Both +3 and +4
Answer: (D) Both +3 and +4
Q37. Which transition element is known as coinage metal?
🔵 (A) Fe
🟢 (B) Cu
🟠 (C) Ni
🔴 (D) Cr
Answer: (B) Cu
Q38. The spin-only magnetic moment of d⁵ high-spin complex is:
🔵 (A) 1.73 BM
🟢 (B) 2.83 BM
🟠 (C) 3.87 BM
🔴 (D) 5.92 BM
Answer: (D) 5.92 BM
Q39. Which ion is most stable in aqueous solution?
🔵 (A) Fe³⁺
🟢 (B) Co³⁺
🟠 (C) Mn³⁺
🔴 (D) Ti³⁺
Answer: (A) Fe³⁺
Q40. Which lanthanoid oxide is most basic?
🔵 (A) La₂O₃
🟢 (B) Gd₂O₃
🟠 (C) Lu₂O₃
🔴 (D) CeO₂
Answer: (A) La₂O₃

🔹 JEE Advanced Level (Q41–Q50)
Q41. Which of the following explains greater range of oxidation states in actinoids compared to lanthanoids?
🔵 (A) Poor shielding of 4f electrons
🟢 (B) Comparable energies of 5f, 6d, 7s orbitals
🟠 (C) Greater electronegativity
🔴 (D) Smaller size
Answer: (B) Comparable energies of 5f, 6d, 7s orbitals
Q42. Which of the following pairs has nearly identical radii due to lanthanoid contraction?
🔵 (A) Ti and Zr
🟢 (B) Zr and Hf
🟠 (C) V and Nb
🔴 (D) Fe and Ru
Answer: (B) Zr and Hf
Q43. Which actinoid shows +7 oxidation state?
🔵 (A) U
🟢 (B) Np
🟠 (C) Pu
🔴 (D) Am
Answer: (B) Np
Q44. The high enthalpy of atomisation in transition metals is due to:
🔵 (A) Weak metallic bonding
🟢 (B) Involvement of multiple valence orbitals in bonding
🟠 (C) Small nuclear charge
🔴 (D) Low density
Answer: (B) Involvement of multiple valence orbitals in bonding
Q45. Which electronic configuration corresponds to a colourless ion?
🔵 (A) d⁵
🟢 (B) d⁰
🟠 (C) d¹
🔴 (D) d⁹
Answer: (B) d⁰
Q46. Which of the following is true about Eu²⁺ and Yb²⁺?
🔵 (A) Stabilised by f⁷ and f¹⁴ respectively
🟢 (B) Both unstable in water
🟠 (C) Both are strong oxidants
🔴 (D) Both prefer +3 always
Answer: (A) Stabilised by f⁷ and f¹⁴ respectively
Q47. Which of the following explains catalytic activity of transition metals?
🔵 (A) Variable oxidation states
🟢 (B) Availability of vacant orbitals
🟠 (C) Adsorption on surface
🔴 (D) All of these
Answer: (D) All of these
Q48. Which of the following lanthanoids is used in lasers?
🔵 (A) Nd
🟢 (B) Sm
🟠 (C) Tb
🔴 (D) Eu
Answer: (A) Nd
Q49. The electronic configuration of Lr (Z=103) is:
🔵 (A) [Rn] 5f¹⁴ 6d¹ 7s²
🟢 (B) [Rn] 5f¹³ 6d² 7s²
🟠 (C) [Rn] 5f¹⁴ 7s²
🔴 (D) [Rn] 5f¹⁰ 6d³ 7s²
Answer: (A) [Rn] 5f¹⁴ 6d¹ 7s²
Q50. Which is the correct reason for decreasing basicity of lanthanoid hydroxides from La(OH)₃ to Lu(OH)₃?
🔵 (A) Decrease in ionic size increases polarising power
🟢 (B) Increase in ionic size decreases polarising power
🟠 (C) Increase in nuclear charge reduces covalency
🔴 (D) Increase in hydration energy
Answer: (A) Decrease in ionic size increases polarising power

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