Which of the following elements does not react with hot concentrated sulphuric acid?

Aqua regia is used for dissolving noble metals ($Au$,$Pt$,etc.). The gas evolved in this process is:

Enlist the main uses of nitrogen.

Which reaction$(s)$ among the following produce dinitrogen?
$1. NH_4Cl(aq) + NaNO_2(aq) \longrightarrow$
$2. NH_2CONH_2 + 2H_2O \longrightarrow$
$3. Ba(N_3)_2 \longrightarrow$
$4. NH_4Cl + Ca(OH)_2 \longrightarrow$

What are the number of $P - O - P$ bridges in phosphorus pentoxide and phosphorus trioxide,respectively?

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,$PbI_4$.