Explanation

(c)
${CN}^{-}$ is a better complexing agent (C) as well as a reducing agent(A)
Thus, properties (A) and (C) are shown.
Property (C ):${Ni}^{2 +} + 4{CN}^{-}\ \longrightarrow \left\lbrack Ni(CN)_{4} \right\rbrack^{2 -}$
Property(A): $\begin{matrix}
II\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ I\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \\
CuCl2 + 5KCN \longrightarrow K_{3}\lbrack Cu(CN)_{4}\rbrack + \frac{1}{2}(CN)_{2} + 2KCl
\end{matrix}$
($CN^{-}\ reduces\ Cu^{2 +}\ to\ Cu^{+}$)