Among N i C O 4 2 - , N i C N 4 2 - and N i C l 4 2 - species, the hybridisation states of the Ni atom are respectively: (Atomic no. of Ni=28)

Step-by-step solution

In N i C O 4 , nickel is sp 3 -hybridised because in it the oxidation state of Ni is zero. In N i C N 4 2 - , n i c k e l i s p r e s e n t as N i 2 + , so its configuration= 1 s 2 , 2 s 2 2 p 6 , 3 s 2 3 p 6 3 d 8 C N - is strong field ligand, hence it makes N i 2 + electrons to be paired up. In N i C l 4 2 - s p e c i e s , n i c k e l i s p r e s e n t as N i 2 + , so its configuration= 1 s 2 , 2 s 2 2 p 6 , 3 s 2 3 p 6 3 d 8 C l - is weak field ligand, hence N i 2 + electrons are not paired.