Which compound is formed when an excess of $KCN$ is added to an aqueous solution of copper sulphate?

Copper sulphate solution reacts with $KCN$ to give

$CuSO_4$ solution reacts with excess of $KCN$ solution to form:

The number of moles of $NH_{3}$ that must be added to $2 \, L$ of $0.80 \, M \, AgNO_{3}$ in order to reduce the concentration of $Ag^{+}$ ions to $5.0 \times 10^{-8} \, M$ ($K_{\text{formation}}$ for $[Ag(NH_{3})_{2}]^{+} = 1.0 \times 10^{8}$) is ...... . (Nearest integer)
[Assume no volume change on adding $NH_{3}$ ]

Which among the following is a correct decreasing order of thermodynamic stability of the complexes?

Which of the following ions forms the most stable complex compound?