The correct option is C [ZnBr4]2− is tetrahedral and diamagnetic
[Cu(CN4)]3− has tetrahedral geometry and sp3 hybridization.
[Ni(CN6)]4− is octahedral and Ni had sp3d2 hybridization.
[Cr(NH3)6]3+ has octahedral geometry and d2sp3 hybridization.
[ZnBr4]2− is tetrahedral and diamagnetic
Zn+2,d10sp3 hybridization so tetrahedral geometry.
And it has zero unpaired electron so diamagnetic.