JEE Main · 2024 · 01 Feb 2024 · Shift 2 · d and f Block Elements

Which of the following compounds show colour due to d-d transition?

(A) $CuSO_{4} \cdot 5 H_{2} O$ ✓ Correct
(B) $K_{2} Cr_{2} O_{7}$
(C) $K_{2} CrO_{4}$
(D) $KMnO_{4}$

Answer: (A)

Solution

A d–d transition requires a partially filled d-subshell with at least one unpaired electron, so an electron can be excited between the split d-orbitals.

C u^{2 +}

C u S O_{4} \cdot 5 H_{2} O

has configuration

3 d^{9}

, with one unpaired electron, and its blue colour comes from a d–d transition.

K_{2} C r_{2} O_{7}

K_{2} C r O_{4}

, and

K M n O_{4}

contain

C r^{6 +}

and

M n^{7 +}

, both

3 d^{0}

with no d-electrons at all; their colours arise from ligand-to-metal charge transfer, not from a d–d transition.

JEE Main · 2024 · 01 Feb 2024 · Shift 2 · Single correct option

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