Which of the following has the maximum number of unpaired ' d ' electrons?

Step-by-step solution

aligned Zn (30)=& [ Ar ] 3 ~d ¹⁰, 4 ~s ² Zn ²⁺ &=[ Ar ] 3 ~d ¹⁰ (no unpaired electron) Fe (26) &=[ Ar ] 3 ~d ⁶, 4 ~s ² Fe ²⁺ &=[ Ar ] 3 ~d ⁶ (four unpaired electrons) aligned aligned Ni (28) &=[ Ar ] 3 ~d ⁸, 4 ~s ² Ni ³⁺ &=[ Ar ] 3 ~d ⁷ (three unpaired electrons) aligned aligned Cu (29) &=[ Ar ] 3 ~d ¹⁰, 4 ~s ¹ Cu ⁺ &=[ Ar ] 3 ~d ¹⁰ (no unpaired electron) aligned