Which among the following metal complexes exhibits optical activity? ($AA$ = bidentate ligand; $A, X$ = monodentate ligands)

Assertion : $[Fe(CN)_6]^{3-}$ is weakly paramagnetic while $[Fe(CN)_6]^{4-}$ is diamagnetic.
Reason : $[Fe(CN)_6]^{3-}$ has $+3$ oxidation state while $[Fe(CN)_6]^{4-}$ has $+2$ oxidation state.

Which of the following compounds is not coloured?

$26.7 \ g$ of a compound with the formula $PtCl_2Br_2 \cdot 6H_2O$ is taken for analysis. This compound exhibits stereoisomerism,and a total of $3$ stereoisomers exist. Find the loss in mass (in $g$) when the given amount of the compound is treated with concentrated $H_2SO_4$. (Molar mass: $PtCl_2Br_2 \cdot 6H_2O = 534 \ g \ mol^{-1}$)

$[Co(en)_3]^{3+}$ ion is expected to show

The correct structures of trans-$[NiBr_{2}(PPh_{3})_{2}]$ and meridional-$[Co(NH_{3})_{3}(NO_{2})_{3}]$,respectively,are