The number of geometrical isomers for $[Pt(NH_3)_2Cl_2]$ is

For a metal ion,the calculated magnetic moment is $4.90 \ BM$. This metal ion has $........$ number of unpaired electrons.

Draw the structures of optical isomers of:
$(i)$ $[Cr(C_2O_4)_3]^{3-}$
$(ii)$ $[PtCl_2(en)_2]^{2+}$
$(iii)$ $[Cr(NH_3)_2Cl_2(en)]^{+}$

The complex compounds $[Co(NH_3)_5 SO_4] Br$ and $[Co(NH_3)_5 Br] SO_4$ are

Which one of the following compounds is not coloured?

Among $(i)$ $[Cr(en)_{3}]^{3+}$,$(ii)$ $trans-[Cr(en)_{2}Cl_{2}]^{+}$,$(iii)$ $cis-[Cr(en)_{2}Cl_{2}]^{+}$,$(iv)$ $[Co(NH_{3})_{4}Cl_{2}]^{+}$,the optically active complexes are: