Zn+ (at.no. 30) =1s2,2s2,2p6 (no unpairedd-electrons) 3s23p63d104s1 Fe2+ (at.no.-26) 1s2,2s22p6,3s23p63d6
N3+ (at. no.=7) =1s2,2s22p0 ( no unpaired d-electrons) Cu+(at.no. = 29) 1s2,2s22p6,3s23p63d10 ( no unpaired d-electrons) So, maximum number of unpaired electrons are present in Fe2+