The possible number of stereoisomers for $[Co(en)_2Cl_2]^+$ is

Which of the following will have three stereoisomeric forms?
$(i)$ $[Cr(NO_3)_3(NH_3)_3]$
$(ii)$ $K_3[Co(C_2O_4)_3]$
$(iii)$ $K_3[CoCl_2(C_2O_4)_2]$
$(iv)$ $[CoBrCl(en)_2]$

Of the following,which is diamagnetic in nature?

Which of the following compounds will exhibit coordination isomerism?

For the complex ion $[Ni(Cl)_4]^{2-}$, what is the theoretical value of the magnetic moment (in $BM$)?

The number of enantiomeric pairs possible for the complex having general formula $[M(AB)_3]$ with coordination number $6$ is