The d- and f-Block Elements: Class 12 Important Questions with Answers

Practice set: test yourself

Try every question before looking at the answers below. 64 or more out of 80 means you are ready for the board.

C. Very short answer (1 mark each)

1. Define a transition element.
2. Why is Cr 3d⁵4s¹?
3. Name the ore of chromium.
4. Give the formula of the manganate ion.
5. What is an interstitial compound?
6. Give one use of misch metal.
7. Which lanthanoid shows +4?
8. Why is Ti⁴⁺ colourless?
9. What is disproportionation?
10. Last element of the actinoids.

D. Short answer I (2 marks each)

1. Calculate μ (spin-only) for Fe²⁺ and Ni²⁺.
2. Why are Mn²⁺ compounds more stable than Fe²⁺ towards oxidation?
3. Complete: Cr₂O₇²⁻ + 3Sn²⁺ + 14H⁺ →
4. Complete: 2MnO₄⁻ + 5H₂S + 6H⁺ →
5. Why is E°(Cu²⁺/Cu) positive?
6. Why do transition metals form alloys?
7. Give two consequences of lanthanoid contraction.
8. Why is Cr²⁺ reducing while Mn³⁺ is oxidising?

Rough work

E. Short answer II (3 marks each)

1. Describe the preparation of K₂Cr₂O₇ from chromite ore with equations.
2. Write the ionic equations of acidified KMnO₄ with Fe²⁺, oxalate and I⁻.
3. Explain: (a) Zn²⁺ is colourless; (b) Mn shows +7; (c) Sc shows only +3.
4. Compare lanthanoids and actinoids (three points).
5. Explain why transition metals and their compounds are good catalysts, with two examples.
6. Explain the variation of E°(M²⁺/M) across the 3d series.

F. Long answer (5 marks each)

1. (a) How is KMnO₄ prepared from pyrolusite? (b) Write its reactions in acid with SO₂ and in neutral solution with I⁻. (c) Why is KMnO₄ not used with HCl in titrations?
2. (a) What is lanthanoid contraction? Its cause and consequences. (b) Why do actinoids show more oxidation states? (c) Why is Ce⁴⁺ an oxidant?

G. HOTS (higher-order thinking)

1. Why does the blue colour of CuSO₄ solution disappear when Zn is added?
2. Why is Co³⁺ unstable in water but stable in [Co(NH₃)₆]³⁺?
3. Why is the +2 state of Ti hard to keep in water?
4. Why are Cd and Hg salts usually colourless?

20 MCQs

1. Not a transition element
   (a) Sc (b) Cu (c) Zn (d) Fe
2. Configuration of Cr
   (a) 3d⁵4s¹ (b) 3d⁴4s² (c) 3d⁶ (d) 3d³4s²4p¹
3. Colourless ion
   (a) Cu²⁺ (b) Ti³⁺ (c) Fe³⁺ (d) Sc³⁺
4. μ of Ti³⁺
   (a) 2.83 (b) 1.73 (c) 3.87 (d) 0
5. Highest oxidation state of Mn
   (a) +6 (b) +7 (c) +5 (d) +8
6. Strong reducing d⁴ ion
   (a) Mn³⁺ (b) Co⁵⁺ (c) Fe⁴⁺ (d) Cr²⁺
7. Positive E°(M²⁺/M)
   (a) Cu (b) Zn (c) Fe (d) Ni
8. MnO₂ + KOH + O₂ gives
   (a) KMnO₄ (b) Mn₂O₇ (c) K₂MnO₄ (d) MnO
9. Orange dichromate in alkali gives
   (a) Cr³⁺ (b) Cr (c) CrO₃ (d) CrO₄²⁻
10. Electrons taken by MnO₄⁻ in acid
    (a) 3 (b) 5 (c) 1 (d) 7
11. Acidic oxide
    (a) MnO (b) CrO (c) Mn₂O₇ (d) Cu₂O
12. Lanthanoid with +4
    (a) Ce (b) Eu (c) Yb (d) La
13. Cause of lanthanoid contraction
    (a) radioactivity (b) poor 4f shielding (c) 6s filling (d) high mass
14. Zr and Hf similar because of
    (a) inert pair (b) d–d transition (c) lanthanoid contraction (d) hydration
15. Paramagnetic species
    (a) MnO₄⁻ (b) Cu⁺ (c) Zn²⁺ (d) MnO₄²⁻
16. Misch metal is used in
    (a) lighter flints (b) jewellery (c) wires (d) batteries
17. Actinoids show many states because of
    (a) close 5f, 6d, 7s energies (b) radioactivity (c) large mass (d) small size
18. Cu⁺ in water
    (a) is stable (b) forms Cu²⁺ only on heating (c) is oxidised by air only (d) disproportionates
19. Interstitial compounds are
    (a) soft (b) hard (c) ionic (d) stoichiometric
20. Lowest ΔaH in 3d
    (a) Mn (b) Cu (c) Zn (d) Sc

1 (c) · 2 (a) · 3 (d) · 4 (b) · 5 (b) · 6 (d) · 7 (a) · 8 (c) · 9 (d) · 10 (b) · 11 (c) · 12 (a) · 13 (b) · 14 (c) · 15 (d) · 16 (a) · 17 (a) · 18 (d) · 19 (b) · 20 (c)

Assertion–Reason (6)

(a) Both true, R explains A. (b) Both true, R does not explain A. (c) A true, R false. (d) A false, R true.

1. A: Zn²⁺ salts are white. R: Zn²⁺ has a completely filled 3d subshell.
2. A: Mn³⁺ is a strong oxidising agent. R: Mn²⁺ has a stable half-filled d⁵ configuration.
3. A: KMnO₄ is purple. R: KMnO₄ has unpaired d electrons.
4. A: Transition metals have high enthalpies of atomisation. R: They have many unpaired electrons.
5. A: Lanthanoids are difficult to separate. R: Lanthanoids are radioactive.
6. A: Cu⁺ is diamagnetic. R: Cu⁺ is 3d¹⁰.

Key: 1 (a) · 2 (a) · 3 (c) · 4 (a) · 5 (c) · 6 (a)

Answers to the practice set