How many optical isomers are possible for the complex $[Pt(NH_3)_2(CN)_2]$?

Out of the following two coordination entities,which is chiral (optically active)?
$(a)$ $cis-[CrCl_{2}(ox)_{2}]^{3-}$
$(b)$ $trans-[CrCl_{2}(ox)_{2}]^{3-}$

The magnetic moment of the complex $[Ni(NH_3)_6]Cl_2$ is

The complex(es),which can exhibit the type of isomerism shown by $[Pt(NH_3)_2 Br_2]$,is(are) [en $= H_2 NCH_2 CH_2 NH_2$ ]
$(A)$ $[Pt(en)(SCN)_2]$
$(B)$ $[Zn(NH_3)_2 Cl_2]$
$(C)$ $[Pt(NH_3)_2 Cl_4]$
$(D)$ $[Cr(en)_2(H_2 O)(SO_4)]^{+}$

Which of the following complexes possesses a meridional $(mer)$ isomer?

Observe the following complex ions:

Complex Ion	Label
$[Mn(CN)_6]^{3-}$	$A$
$[Fe(CN)_6]^{3-}$	$B$
$[CoF_6]^{3-}$	$C$
$[Co(C_2O_4)_3]^{3-}$	$D$

Identify the option in which the unpaired electrons in the complex ions are in correct increasing order.