Which of the following forms cyclic silicones on hydrolysis?

In the following reaction,identify the nature of the product formed by the complete hydrolysis of the underlined atom at $R.T.$:
$\underline{P}OCl_3 + H_2O \longrightarrow H_3PO_4 + HCl$

The gas which turns lime water milky is

$PbI_4$ does not exist because

The correct statements with respect to halides of group $14$ elements are:
$I$. Both $CCl_4$ and $SiCl_4$ undergo hydrolysis
$II$. $GeX_4$ is more stable than $GeX_2$
$III$. $PbX_4$ is less stable than $PbX_2$
$IV$. Stability of dihalides decreases down the group.

Name the type of the structure of silicate in which one oxygen atom of $[SiO_4]^{4-}$ is shared?