$PbCl_{2}$ is insoluble in cold water. Addition of $HCl$ increases its solubility due to

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:

The overall stability constant of the complex ion $[Cu(NH_3)_4]^{2+}$ is $2.1 \times 10^{13}$. The overall dissociation constant is $y \times 10^{-14}$. Then $y$ is ....... .(Nearest integer)

Copper sulphate solution reacts with $KCN$ to give

The $\pi-$acid ligand which uses its $d-$orbital during synergic bonding in its complex compound is:

Some salts,although containing two different metallic elements,give a test for only one of them in solution. Such salts are: