Which of the following pairs of elements form amphoteric oxides?

Provide information about silicon compounds (silicates).

Identify $X, Y$ and $Z$ in the following reaction: $2 CH_3Cl + X \xrightarrow[570 \ K]{Y} Z$

Select the member$(s)$ of group $14$ that $(i)$ forms the most acidic dioxide,$(ii)$ is commonly found in $+2$ oxidation state,$(iii)$ used as semiconductor.

Assertion : $SiF_6^{2-}$ is known but $SiCl_6^{2-}$ is not.
Reason : Size of fluorine is small and its lone pair of electrons interacts with $d-$orbitals of $Si$ strongly.

In the following reaction,identify the nature of the product formed by the complete hydrolysis of the underlined atom at $R.T$:
$H_6\underline{Si}_2O_7 + H_2O \longrightarrow H_4SiO_4$