Among the following,the $\pi$-acid ligand is

Give the correct order of electrical conductivity of aqueous solution of the following complexes:
$A$. $[Pt(NH_3)_6]Cl_4$
$B$. $[Cr(NH_3)_6]Cl_3$
$C$. $[Co(NH_3)_4Cl_2]Cl$
$D$. $K_2[PtCl_6]$

$PtCl_4 \cdot 6H_2O$ can exist as a hydrated complex. Its $1 \ m$ aqueous solution has a depression in freezing point of $3.72 \ ^\circ C$. Assuming $100\%$ ionization and $K_f \ (H_2O) = 1.86 \ ^\circ C \ kg \ mol^{-1}$,the correct formula for the complex is:

The reaction of $CuSO_4$ with excess $KCN$ solution leads to the formation of:

When $0.1 \ mole$ of $CoCl_3(NH_3)_5$ is treated with excess of $AgNO_3$,$0.2 \ mole$ of $AgCl$ are obtained. The conductivity of the solution will correspond to:

Complex $A$ has a composition of $H_{12}O_{6}Cl_{3}Cr$. If the complex on treatment with conc. $H_{2}SO_{4}$ loses $13.5\%$ of its original mass,the correct molecular formula of $A$ is :
[Given : atomic mass of $Cr = 52 \ amu$ and $Cl = 35.5 \ amu$]