How many of the following complexes have unpaired electrons on their central atom

CHEMISTRY · Subjective · ISC · Chemistry · Coordination Compounds · Coordination Compounds

Problem

How many of the following complexes have unpaired electrons on their central atom ?

[\text{Ni}(\text{CO})_4]

[\text{NiCl}_4]^{2-}

[\text{PtCl}_4]^{2-}

[\text{Pt}(\text{CN})_4]^{2-}