$AlF_3$ is soluble in $HF$ only in the presence of $KF$. This is due to the formation of:

Considering the complexes $(i) K_2PtCl_6$,$(ii) PtCl_4 \cdot 2NH_3$,$(iii) PtCl_4 \cdot 3NH_3$,and $(iv) PtCl_4 \cdot 5NH_3$,the molar conductivities in aqueous solution follow the order (in $\Omega^{-1} \ cm^2 \ mol^{-1}$):

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

On treatment of $100 \ mL$ of $0.1 \ M$ solution of $CoCl_3 \cdot 6H_2O$ with excess $AgNO_3$,$1.2 \times 10^{22}$ ions are precipitated. The complex is:

$CuSO_4$ decolourises on addition of $KCN$,the product is

The most stable complex among the following is