Sulphur is most soluble in

The stability of dihalides of $Si, Ge, Sn$ and $Pb$ follows the sequence.

In the following reaction,assign the nature of the product of complete hydrolysis at $R.T.$ for the underlined atom:
$\underline{Si}H_4 + 4H_2O \longrightarrow H_4SiO_4 + 4H_2$

Philosopher's wool when heated with $BaO$ at $1100\,^{\circ}C$ gives a compound. Identify the compound.

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

Explain the following:
$(a)$ $CO_2$ is a gas whereas $SiO_2$ is a solid.
$(b)$ Silicon forms $SiF_6^{2-}$ ion whereas corresponding fluoro compound of carbon is not known.