$\pi$-acid ligands are

Which of the following statements is not correct?

Copper sulphate solution reacts with $KCN$ to give

Which one of the following metal complexes is most stable?

What is the coordination entity formed when excess of aqueous $KCN$ is added to an aqueous solution of copper sulphate? Why is it that no precipitate of copper sulphide is obtained when $H_{2}S_{(g)}$ is passed through this solution?

Considering the complexes $(i) K_2PtCl_6$,$(ii) PtCl_4 \cdot 2NH_3$,$(iii) PtCl_4 \cdot 3NH_3$,and $(iv) PtCl_4 \cdot 5NH_3$,the molar conductivities in aqueous solution follow the order (in $\Omega^{-1} \ cm^2 \ mol^{-1}$):