Select the pair of d-block metals which do not show exceptional elect…

The correct answer is Option (1) → Zn-Cd

The d-block elements have the general configuration (n−1)d^1–10ns^1–2. Because the (n−1)d and ns orbitals are very close in energy, an element whose d subshell is one electron short of half-filled (d⁵) or full (d¹⁰) moves an ns electron into it. Such a configuration is called exceptional.

• Option (1) Zn-Cd — Do not show exceptional configurations. Zn (Z = 30) is [Ar]3d¹⁰4s² and Cd (Z = 48) is [Kr]4d¹⁰5s². The d subshell is already full with two s electrons, just as the normal filling order predicts.

• Option (2) Cr-Cu — Show exceptional configurations. Cr (Z = 24) would be expected as [Ar]3d⁴4s² and Cu (Z = 29) as [Ar]3d⁹4s²; the actual configurations are [Ar]3d⁵4s¹ and [Ar]3d¹⁰4s¹.

• Option (3) Mo–Ag — Show exceptional configurations. Mo (Z = 42) is [Kr]4d⁵5s¹ (half-filled) and Ag (Z = 47) is [Kr]4d¹⁰5s¹ (full).

• Option (4) Pd- Au — Show exceptional configurations. Pd (Z = 46) is [Kr]4d¹⁰5s⁰ and Au (Z = 79) is [Xe]4f¹⁴5d¹⁰6s¹.

NCERT (2026-27 edition):
Electronic Configurations of the d-Block Elements – …