d-Block Elements (the transition metals) is one of the most reliable scoring chapters in JEE Inorganic Chemistry because the question types repeat and they are NCERT-rooted: electronic configuration anomalies, variable oxidation states, magnetic moment, colour, and the chemistry of K₂Cr₂O₇ and KMnO₄. In JEE Main it is a steady 1–2 questions almost every year, usually direct and single-fact. In JEE Advanced it appears most years (1–2 questions) and runs deeper — fused with coordination chemistry, redox stoichiometry of the dichromate/permanganate oxidations, and reasoning on why a property trends the way it does. Because the answers are recall plus one short step, it gives a high marks-per-hour return.

How to Study d-Block Elements (Transition Metals) — In Order

1. Electronic configuration and the Cr/Cu exceptions. Cr is [Ar]3d⁵4s¹ and Cu is [Ar]3d¹⁰4s¹ (half- and fully-filled stability). For ions, remove the 4s electrons before 3d — so Fe²⁺ is 3d⁶, Fe³⁺ is 3d⁵. Everything downstream (magnetic moment, colour, oxidation state) depends on getting this right first.
2. Trends across the 3d series. Atomic/ionic radii (the irregular dip and near-constancy), ionization enthalpy, and why variable oxidation states arise (close 3d/4s energies). These trend questions are pure Main marks.
3. Why coloured and why magnetic. Colour comes from d–d transitions, which need a partially filled d-subshell. Magnetic moment is the spin-only value μ = √(n(n+2)) BM from the number of unpaired electrons. Tie the configuration to both properties.
4. Catalytic, interstitial and alloy behaviour. Variable oxidation states and the ability to adsorb on the surface explain catalysis; small atoms (H, C, N) trapped in the lattice give interstitial compounds; similar radii give alloys. Short, high-yield recall.
5. K₂Cr₂O₇ and KMnO₄ last. Preparation and, above all, their oxidising reactions in acidic and basic medium — with the n-factors. This is the single most examined block in the chapter and ties redox stoichiometry to the inorganic facts.

High-Yield Sub-Topics (most-asked first)

1. Configurations of atoms and ions (remove 4s first). The most frequent Main question. Know the Cr and Cu exceptions, then apply "remove 4s before 3d" for cations: Mn²⁺ = 3d⁵ (μ = 5.92 BM, the maximum for the series), Fe³⁺ = 3d⁵, Cu²⁺ = 3d⁹ (one unpaired, μ = 1.73 BM). A large share of magnetic-moment questions are this one rule plus √(n(n+2)).
2. Spin-only magnetic moment. μ = √(n(n+2)) BM where n = number of unpaired electrons gives the ladder 0, 1.73, 2.83, 3.87, 4.90, 5.92 BM for n = 0–5. Working backward from a given μ to identify the ion (and hence its oxidation state) is a recurring Advanced ask.
3. Origin of colour — d–d transition vs charge transfer. Coloured because of d–d transitions requires a partially filled d-subshell. KMnO₄ (Mn is +7, d⁰) and K₂Cr₂O₇ (Cr is +6, d⁰) have NO d electrons yet are intensely coloured — the colour there is ligand-to-metal charge transfer, not a d–d transition. This distinction is examined directly.
4. KMnO₄ and K₂Cr₂O₇ as oxidisers. In acidic medium MnO₄⁻ → Mn²⁺ (gain of 5 e⁻, n-factor 5) and Cr₂O₇²⁻ → 2Cr³⁺ (gain of 6 e⁻, n-factor 6). In neutral/basic medium MnO₄⁻ → MnO₂ (3 e⁻). Their reactions with Fe²⁺, oxalate, iodide and H₂S, plus the equivalent-weight calculations, are guaranteed marks.

Mistakes Students Repeatedly Make

• Removing a 3d electron before a 4s electron when writing an ion configuration. For transition-metal cations the 4s electrons leave first — Fe²⁺ is 3d⁶, not 3d⁴4s².
• Saying KMnO₄ and K₂Cr₂O₇ are coloured because of d–d transitions. Both metals are d⁰ in those species; the colour is charge-transfer, and assuming d–d here is a classic trap.
• Assuming the highest possible oxidation state is the most stable. Stability depends on the element — Mn(VII) and Cr(VI) are strong oxidisers (not "stable"), while Mn(II) and Fe(III) are the genuinely stable states.
• Treating Zn, Cd and Hg as typical transition metals. They are d¹⁰ in both the atom and their common ions, so they show no d–d colour and are diamagnetic — by the strict definition they are not transition elements.