The square-planar complex of type [Mabcd]nt, where all four ligands are different, has 3 geometrical isomers. But if one of the ligands is ambidentate, then 2×3=6 geometrical isomers are possible.
Here, two ligands are ambidentate, then 4×3=12 geometrical isomers are possible.
In our example, both NO2−and SCN−are ambidentate ligands.
Hence option B is correct.
The total number of possible isomers for square-planar [Pt(Cl)(NO2)(NO3)(SCN)]2− is 12.