Which one of the following transition metal ions is diamagnetic?

Step-by-step solution

Transition metal ion having absence of unpaired electron is diamagnetic. (1) Co ²⁺=[ Ar ] 3 d^7 (three unpaired electrons) (2) Ni ²⁺=[ Ar ] 3 d^8 (two unpaired electrons) (3) Cu ²⁺=[ Ar ] 3 d^9 (one unpaired electron) (4) Zn ²⁺=[ Ar ] 3 d¹⁰ (no unpaired electron) Thus, Zn ²⁺ is diamagnetic.