Which of the following complexes does not give a precipitate with $AgNO_3$ solution?

Silver chloride dissolves in excess of $NH_4OH$. The cation present in this solution is

$FeSO_4$ solution mixed with $(NH_4)_2SO_4$ solution in $1:1$ molar ratio gives the test of $Fe^{2+}$ ion,but $CuSO_4$ solution mixed with aqueous ammonia in $1:4$ molar ratio does not give the test of $Cu^{2+}$ ion. Explain why?

Which of the following is non-conducting?

Assertion : $NF_3$ is a weaker ligand than $N(CH_3)_3$.
Reason : $NF_3$ ionizes to give $F^{-}$ ions in aqueous solution.

Assign $A, B, C, D$ for the type of observation in the following reaction:
$CuSO_4 + KCN \text{ (excess)} \longrightarrow K_3[Cu(CN)_4] + \frac{1}{2}(CN)_2$