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

Given below are two statements:
Statement $I$ : $N(CH_3)_3$ and $P(CH_3)_3$ can act as ligands to form transition metal complexes.
Statement $II$: As $N$ and $P$ are from same group,the nature of bonding of $N(CH_3)_3$ and $P(CH_3)_3$ is always same with transition metals.
In the light of the above statements,choose the most appropriate answer from the options given below:

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

Which of the following cations forms the least stable complex with the same ligand?

An aqueous solution of $FeSO_4$ gives tests for both $Fe^{2+}$ and $SO_4^{2-}$ ions,but after the addition of an excess of $KCN$,the solution ceases to give a test for $Fe^{2+}$. This is due to the formation of:

The cation that does not form an amine complex with excess of ammonia is