The correct option is D [Cr(NH3)6]Cl3
1. [Ni(CO)4]
Ni:28:[Ar]3d84s2Ni0:28:[Ar]3d104s0
CO is a strong field ligand, it forces pairing. Hence, this is diamagnetic.
2. K2[Ni(CN)4]
Ni:28:[Ar]3d84s2Ni2+:26:[Ar]3d84s0
CN− is a strong field ligand, it forces pairing. Hence, this is diamagnetic.
3. K3[CoF6]
Co:27:[Ar]3d74s2Co3+:24:[Ar]3d64s0
F− is a weak field ligand, it does not force pairing. Hence, this is paramagnetic.
4. [Cr(NH3)6]Cl3
Cr:24:[Ar]3d44s2Cr3+:21:[Ar]3d34s0
NH3 is a strong field ligand, it forces pairing. But, there is only 1 unpaired electron. So this is paramagnetic.