Answer the question on the basis of passage given below:
Transition metals form a large number of complexes or coordination compounds in which the metal atoms are bound to a number of anions or neutral molecules. The valence bond theory explains the formation, magnetic behaviour and geometrical shapes while the crystal field theory explains the effect of different crystal fields on the degeneracy of d-orbital energies of the central metal atom/ion. This provides for the quantitative estimation of orbital separation energies, magnetic moments and spectral and stability parameters.
Match List I (Species/ions) with List II (Colour)
| List I | List II |
| (A) \(Mn^{2+}\) | (I) Yellow |
| (B) \(Fe^{3+}\) | (II) Green |
| (C) \(Ni^{2+}\) | (III) Blue |
| (D) \(Cu^{2+}\) | (IV) Pink |
Choose the correct answer from the options given below:
Answer & explanation
Correct answer: option 2
The correct answer is Option (2) → (A)-(IV), (B)-(I), (C)-(II), (D)-(III)
Transition metal ions with partly filled d orbitals are coloured: the hydrated ion absorbs light of one colour for a d–d transition, and the complementary colour is seen. The colour depends on the d-electron count and the ligand (here water).
(A) \( \ce{Mn^{2+}} \) — This matches (IV) Pink. Mn (Z = 25) [Ar]3d54s2 → \( \ce{Mn^{2+}} \) 3d5; \( \ce{[Mn(H2O)6]^{2+}} \) is pale pink.
(B) \( \ce{Fe^{3+}} \) — This matches (I) Yellow. Fe (Z = 26) [Ar]3d64s2 → \( \ce{Fe^{3+}} \) (two 4s and one 3d electron removed) 3d5; the hydrated ion is yellow.
(C) \( \ce{Ni^{2+}} \) — This matches (II) Green. Ni (Z = 28) [Ar]3d84s2 → \( \ce{Ni^{2+}} \) 3d8; \( \ce{[Ni(H2O)6]^{2+}} \) is green.
(D) \( \ce{Cu^{2+}} \) — This matches (III) Blue. Cu (Z = 29) [Ar]3d104s1 → \( \ce{Cu^{2+}} \) 3d9; the hydrated ion is blue (as in \( \ce{CuSO4} \)·\( \ce{5H2O} \)).
Shortcut: (A)-(IV) appears only in Option (2).
NCERT (2026-27 edition):
Formation of Coloured Ions – …
