NEET Chemistry — d and f Block Elements Complete Chapter Guide

Chapter Overview & Weightage

d and f Block Elements covers transition metals and inner transition metals. NEET focuses on electronic configurations, oxidation states, magnetic properties, and colour of compounds. It is mostly factual — the student who memorises smartly scores well.

d and f Block carries 3-4% weightage in NEET with 2-3 questions. Electronic configuration, variable oxidation states, and magnetic properties dominate.

Year	NEET Q Count	Key Topics Tested
2025	2	Oxidation states, electronic configuration
2024	2	Magnetic moment, colour
2023	3	Lanthanoid contraction, KMnO4
2022	2	Configuration of ions, catalytic activity
2021	2	Interstitial compounds, alloy formation

graph TD
    A[d and f Block] --> B[Transition Metals: 3d series]
    A --> C[Properties]
    A --> D[Lanthanoids]
    A --> E[Actinoids]
    C --> F[Variable Oxidation States]
    C --> G[Colour and Magnetism]
    C --> H[Catalytic Activity]
    C --> I[Complex Formation]
    B --> J[Electronic Configuration]
    B --> K[Important Compounds: KMnO4, K2Cr2O7]
    D --> L[Lanthanoid Contraction]

Key Concepts You Must Know

Tier 1 (Always asked)

Electronic configuration of 3d elements and their ions (Cr, Cu exceptions)
Oxidation states: most stable and highest for each element
Magnetic moment: $\mu = \sqrt{n(n+2)}$ BM where $n$ = unpaired electrons
Colour of transition metal ions (d-d transitions)

Tier 2 (Frequently asked)

Lanthanoid contraction: cause and consequences
KMnO $_4$ and K $_2$ Cr $_2$ O $_7$ : preparation, structure, reactions
Catalytic activity of transition metals
Interstitial compounds and alloy formation

Tier 3 (Occasional)

Ionization enthalpy trends across 3d series
Actinoids vs lanthanoids comparison
Standard electrode potentials of 3d metals

Important Formulas

\mu = \sqrt{n(n+2)} \text{ BM}

Ion	Config	Unpaired e $^-$	$\mu$ (BM)
Ti $^{3+}$	3d $^1$	1	1.73
V $^{3+}$	3d $^2$	2	2.83
Cr $^{3+}$	3d $^3$	3	3.87
Mn $^{2+}$	3d $^5$	5	5.92
Fe $^{2+}$	3d $^6$	4	4.90
Fe $^{3+}$	3d $^5$	5	5.92
Cu $^{2+}$	3d $^9$	1	1.73
Zn $^{2+}$	3d $^{10}$	0	0 (diamagnetic)

Most common: +2 (all), +3 (Sc to Co)

Highest oxidation state increases up to Mn (+7), then decreases.

Maximum OS = group number up to Mn. Beyond Mn, d-electrons become too tightly held.

Cr: +2, +3, +6 (K $_2$ Cr $_2$ O $_7$ )

Mn: +2, +4, +7 (KMnO $_4$ )

Zn $^{2+}$ and Cu $^+$ are colourless because they have completely filled d-orbitals (d $^{10}$ ). Colour requires d-d transitions, which need at least one empty and one filled d-orbital. Sc $^{3+}$ (d $^0$ ) is also colourless for the same reason — no d-electron to transition.

Solved Previous Year Questions

PYQ 1 — NEET 2024

Problem: The magnetic moment of a divalent ion in aqueous solution is 5.92 BM. The ion is:

Solution:

$\mu = \sqrt{n(n+2)} = 5.92$ gives $n(n+2) = 35$ , so $n = 5$ .

We need a divalent (M $^{2+}$ ) ion with 5 unpaired d-electrons. That is $d^5$ configuration.

Mn $^{2+}$ : [Ar] 3d $^5$ — five unpaired electrons. Answer: Mn $^{2+}$

Fe $^{3+}$ is also d $^5$ but it is trivalent, not divalent.

PYQ 2 — NEET 2023

Problem: Lanthanoid contraction is caused by:

Solution:

The poor shielding effect of 4f electrons. As we move across the lanthanoid series, electrons are added to the 4f subshell which has poor shielding ability. The nuclear charge increases, but the 4f electrons do not effectively screen each other. Result: gradual decrease in atomic and ionic radii across the series.

Consequence: Elements after lanthanoids (Hf, Ta, W) have nearly the same radii as their 4d counterparts (Zr, Nb, Mo). This explains why separating Zr/Hf and Nb/Ta is extremely difficult.

Difficulty Distribution

Difficulty	% of Questions	What to Expect
Easy	40%	Configuration, magnetic moment calculation
Medium	45%	Oxidation states, colour, lanthanoid contraction
Hard	15%	KMnO4 reactions, inter-element comparisons

Expert Strategy

Week 1: Write out the electronic configuration of all 3d elements (Sc to Zn) and their common ions. Know the exceptions: Cr is [Ar] 3d $^5$ 4s $^1$ and Cu is [Ar] 3d $^{10}$ 4s $^1$ .

Week 2: Properties — magnetic moment, colour, oxidation states. The formula $\mu = \sqrt{n(n+2)}$ is used frequently. Practise identifying ions from their magnetic moments.

Week 3: Important compounds (KMnO $_4$ , K $_2$ Cr $_2$ O $_7$ ) and lanthanoid contraction. These are factual — make concise notes and revise repeatedly.

Common Traps

Trap 1 — Removing electrons from ions. When forming a cation, 4s electrons are removed first (not 3d). Fe [Ar] 3d $^6$ 4s $^2$ becomes Fe $^{2+}$ [Ar] 3d $^6$ (lose 4s $^2$ ), not Fe $^{2+}$ [Ar] 3d $^4$ 4s $^2$ .

Trap 2 — Zn is not always classified as a transition metal. By strict definition, a transition metal must have an incomplete d-subshell in at least one stable oxidation state. Zn $^{2+}$ has d $^{10}$ — complete. So Zn is sometimes excluded. NEET may test this definition.

Trap 3 — Cr $^{3+}$ is the most stable oxidation state of chromium, not Cr $^{6+}$ . While Cr $^{6+}$ exists in K $_2$ Cr $_2$ O $_7$ , it is a strong oxidising agent precisely because it readily accepts electrons to reach the more stable Cr $^{3+}$ .