How many geometrical isomers are possible for the square planar complex $[Pt(NO_2)(Py)(NH_3)(NO_2)]$?

What is the value of spin-only magnetic moment for $Cu^{2+}$ in $BM$?

The pair$(s)$ of coordination complexes/ions exhibiting the same kind of isomerism is(are)
$(A)$ $[Cr(NH_3)_5Cl]Cl_2$ and $[Cr(NH_3)_4Cl_2]Cl$
$(B)$ $[Co(NH_3)_4Cl_2]^+$ and $[Pt(NH_3)_2(H_2O)Cl]^+$
$(C)$ $[CoBr_2Cl_2]^{2-}$ and $[PtBr_2Cl_2]^{2-}$
$(D)$ $[Pt(NH_3)_3(NO_3)]Cl$ and $[Pt(NH_3)_3Cl]Br$

The number of possible stereoisomers for the complex $[Co(en)_2Cl_2]Cl$ is $(en = \text{ethylenediamine})$.

The number of optical isomers exhibited by the iron complex $(A)$ obtained from the following reaction is $.........$
$FeCl_3 + KOH + H_2C_2O_4 \rightarrow A$

The spin-only magnetic moment of $Ni^{2+}$ in an aqueous solution in Bohr magneton $(\mu_B)$ is .......