Chemistry - Complete d-block Question with Solution | TestHub

The correct option is (C) Na > Cu.

Na⁺ has a highly stable noble gas configuration ($1s^{2}2s^{2}2p^6$).

Cu⁺ has a stable fully-filled d-subshell configuration ($[Ar]3d^{10}$).

Removing an electron from a stable noble gas shell ($n=2$) requires much more energy than from a d-subshell ($n=3$) due to smaller size and greater nuclear attraction.

Therefore, the second ionization potential (IP₂) of Na is significantly higher than that of Cu.