The d- and f-Block Elements for NEET UG
Transition metals are coloured, magnetic, good catalysts and show many oxidation states. All of that comes from their partly filled d orbitals.
ChemistryClass 1270 MCQs2 lessons13 flashcards3 memory tricks
Practise The d- and f-Block Elements free
What you'll learn
- Properties of transition metals
Explain variable oxidation states, colour, magnetism and catalytic activity of d-block elements. - Potassium dichromate, potassium permanganate and the f-block
Recall the reactions of K₂Cr₂O₇ and KMnO₄, and compare lanthanoids with actinoids.
Key formulas
| Spin-only magnetic moment | μ = √(n(n + 2)) BM, n = number of unpaired electrons |
|---|
Memory tricks
Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn.
Colour comes from d–d transitions. Sc³⁺ (3d⁰), Ti⁴⁺ (3d⁰), Zn²⁺ and Cu⁺ (3d¹⁰) are colourless.
Acidic: MnO₄⁻ → Mn²⁺ (+7 to +2, 5 electrons). Neutral or weakly alkaline: MnO₄⁻ → MnO₂ (+7 to +4, 3 electrons).
Try 3 NEET-style questions
Q1. When an alkali is added to an orange solution of potassium dichromate, the solution turns yellow because
- Cr₂O₇²⁻ is converted into CrO₄²⁻
- Cr(VI) is reduced to Cr(III)
- chromium is oxidised to Cr(VII)
- Cr(OH)₃ is precipitated
Show answer
Answer: (1) Cr₂O₇²⁻ is converted into CrO₄²⁻
Cr₂O₇²⁻ + 2OH⁻ → 2CrO₄²⁻ + H₂O. Orange dichromate becomes yellow chromate; chromium stays at +6. Adding acid reverses the change.
Q2. Which ion is coloured in aqueous solution?
- Zn²⁺
- Sc³⁺
- Cu²⁺
- Ti⁴⁺
Show answer
Answer: (3) Cu²⁺
Cu²⁺ (3d⁹) has an unpaired d electron and shows d–d transitions (blue).
Q3. Lanthanoid contraction is mainly due to
- Increase in the number of shells
- Poor shielding by 4f electrons
- Large shielding by 5s electrons
- Decrease in nuclear charge
Show answer
Answer: (2) Poor shielding by 4f electrons
4f electrons shield the nuclear charge poorly, so the effective nuclear charge rises and sizes shrink along the series.
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