Which of the following statement is true ?
a. In [PtCl2(NH3)2]2+ the *cis* form is optically inactive while *trans* form is optically active
b. In [Fe(C2O4)3]3− , geometrical isomerism does not exist while optical isomerism exists
c. In *Mabcd*, square planar complexes show both optical as well as geometrical isomerism
d. In *Mabcd* tetrahedral complex, optical isomerism cannot be observed