The total number of possible isomers for $[Cu^{II}(NH_3)_4] [Pt^{II}Cl_4]$ is..........

The existence of two different coloured complexes with the composition of $[Co(NH_3)_4Cl_2]^+$ is due to

Which of the following complexes exhibits both geometric and optical isomerism?

Which of the following statements is not correct?

In an experiment,$m$ grams of a compound $X$ (gas/liquid/solid) taken in a container is loaded in a balance as shown in figure $I$ below. In the presence of a magnetic field,the pan with $X$ is either deflected upwards (figure $II$),or deflected downwards (figure $III$),depending on the compound $X$. Identify the correct statement$(s)$:
$(A)$ If $X$ is $H_2O_{(l)}$,deflection of the pan is upwards.
$(B)$ If $X$ is $K_4[Fe(CN)_6]_{(s)}$,deflection of the pan is upwards.
$(C)$ If $X$ is $O_{2(g)}$,deflection of the pan is downwards.
$(D)$ If $X$ is $C_6H_{6(l)}$,deflection of the pan is downwards.

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