Which of the following species does not exist?

The element $X$ which forms a stable product of the type $XCl_4$ is $....$

Silicon $(IV)$ chloride on hydrolysis gives an acid $X$. The number of $-OH$ groups present in $X$ is

Superphosphate is a mixture of

$SiCl_4$ on hydrolysis forms '$X$' and $HCl$. Compound '$X$' loses water at $1000^{\circ} C$ and gives '$Y$'. Compounds '$X$' and '$Y$' respectively are:

Identify $(P)$ and $(Q)$ in the following reaction:
$2 CH_3 Cl + Si$ $\xrightarrow[570 \ K]{\text{Cu powder}} (P)$ $\xrightarrow{H_2 O} (Q)$ $\longrightarrow \text{Straight chain polymer}$