Calcium phosphide reacts with water to form $Ca(OH)_2$ and $X$. When $X$ is passed into $CuSO_4$ solution,$Y$ and $H_2SO_4$ are formed. What is $Y$?

Which is the correct statement for the given acids?

The correct order of boiling points of hydrides of $15^{th}$ group elements is

Dilute sodium hydroxide does not react with which of the following?

$A$ mixture of ammonia and air at about $800\,^{\circ}C$ in the presence of $Pt$ gauze forms:

Rationalize the given statements and provide chemical reactions:
$1$. Lead $(II)$ chloride reacts with $Cl_2$ to give $PbCl_4$.
$2$. Lead $(IV)$ chloride is highly unstable towards heat.
$3$. Lead is known not to form an iodide,$PbI_4$.