The correct option is
B I and II
Ni(CO)4:
CO is a neutral ligand. Hence, the charge on Ni is zero.
Outer electronic configuration of Ni:3d84s2
![](https://df0b18phdhzpx.cloudfront.net/ckeditor_assets/pictures/1341069/original_4a.png)
It has
sp3 hybridisation. Thus, it is tetrahedral.
Ni(PPh3)2Cl2:
PPh3 is a weak field ligand of pairing of electrons does not occurs.
Here, the
Ni is in +2 oxidation state.
Outer electronic configuration of Ni+2:3d8
![](https://df0b18phdhzpx.cloudfront.net/ckeditor_assets/pictures/1341090/original_4c.png)
It also has
sp3 hybridisation and the geometry is tetrahedral.
K2[Pt(CN)4]
Here,
CN is a strong field ligand so pairing occurs.
The oxidation state of
Pt is +2.
![](https://df0b18phdhzpx.cloudfront.net/ckeditor_assets/pictures/1341094/original_4d.png)
Hence, it is a diamagnetic.
Na3[Co(C2O4)3]:
Oxalate is a bidentate ligand and strong field ligand.
Oxidation state of
Co is +3
Outer electronic configuration of
Co is
3d6
Since, oxalate is strong field ligand all electrons are paired so it is a diamagnetic compound.
Not all geometrical isomers of
[M(AB)b2cd] is optically active.
![](https://df0b18phdhzpx.cloudfront.net/ckeditor_assets/pictures/1341228/original_4f.png)
Thus, correct option is (b).