Superphosphate of lime contains

$P_4O_{10}$ is not used to dry $NH_3$ gas because:

The main reason that $SiCl_{4}$ is easily hydrolysed as compared to $CCl_{4}$ is that

Rationalise the given statements and give 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,$PbI_4$.

Which gas is evolved when $SiO_2$ reacts with sodium carbonate?

Identify the incorrect statement.