Which of the following shows the least value for standard enthalpy of atomization?
Answer & explanation
Correct answer: option 2
The correct answer is Option (2) → Zn
The enthalpy of atomisation is the energy needed to break a metal into free atoms, so it measures the strength of the metallic bonding. In the transition metals both the ns and the unpaired (n−1)d electrons take part in this bonding: the more unpaired electrons available, the stronger the bonding and the higher the enthalpy of atomisation. The values rise to a maximum around the middle of the series and fall towards its end.
Zinc (Z = 30) is [Ar]3d104s2. Its 3d subshell is completely filled, so no d electron is free for metallic bonding; only the two 4s electrons bond the atoms. Its metallic bonding is the weakest in the series, and so is its enthalpy of atomisation, 126 kJ mol−1. So Zn has the least value.
Why the other options are incorrect
Option (1) Mn — Incorrect. Mn (281 kJ mol−1) is low for the middle of the series because its stable half-filled 3d5 set holds its electrons more firmly, but it still has unpaired d electrons and is well above zinc.
Option (3) Cu — Incorrect. Cu (339 kJ mol−1), [Ar]3d104s1, has a filled 3d set, but the d electrons of copper still take part in bonding to some extent, so its value is far above zinc’s.
Option (4) V — Incorrect. V (515 kJ mol−1), [Ar]3d34s2, has three unpaired 3d electrons and one of the highest values in the series.
NCERT (2026-27 edition):
Physical Properties – …
