What is the final product formed when copper sulphate solution reacts with excess $KCN$?

Assertion : $[Al(H_2O)_6]^{3+}$ is a stronger acid than $[Mg(H_2O)_6]^{2+}$.
Reason : Size of $[Al(H_2O)_6]^{3+}$ is smaller than $[Mg(H_2O)_6]^{2+}$ and possesses more effective nuclear charge.

Which of the following complex ions has the least stability?

Cold ferrous sulphate solution on absorption of $NO$ develops brown colour due to the formation of

The deep blue colour produced on adding excess of ammonia to copper sulphate is due to the presence of:

The stability constants for complexes formed by a metal ion $(M^{2+})$ with ligands $NH_3$,$CN^-$,$H_2O$,and $en$ are $10^{11}$,$10^{27}$,$10^{15}$,and $10^8$ respectively. Based on these values,which of the following is correct?