Both [NiCl₄]^2- and [Ni(CO)₄] are tetrahedral, which of these are paramagnetic in nature?

[NiCl₄]^2- 

In [NiCl₄]^2- 

x + 4(-1) = -2

x - 4 = -2

x = -2 + 4 = +2

Ni²⁺: [Ar]3d⁸

In [Ni(CO)₄]

x + 4(0) = 0

x = 0

Ni: [Ar]4s²3d¹⁰

As Cl^- is a weak field ligand, it will not pair up the electrons in 3d-orbital.

Hence, there will be two unpaired electrons and [NiCl₄]^2- is paramagnetic in nature.