The transition element having the least number of unpaired electron i…

The correct answer is Option (1) → Sc

The number of unpaired electrons follows from the ground-state configuration of each atom (Hund’s rule: the 3d orbitals are filled singly first):

• Sc (Z = 21): [Ar] 3d¹ 4s² — 1 unpaired electron

• Ti (Z = 22): [Ar] 3d² 4s² — 2 unpaired electrons

• Cr (Z = 24): [Ar] 3d⁵ 4s¹ — 6 unpaired electrons

• Fe (Z = 26): [Ar] 3d⁶ 4s² — 4 unpaired electrons

So scandium has the least number of unpaired electrons.

NCERT (2026-27 edition):
Electronic Configurations of the d-Block Elements – “… Solution: On the basis of incompletely filled 3d orbitals in case of scandium atom in its ground state (3d¹), it is regarded as a transition element.”