Which of the following units is used to form cross-linked silicone?

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

Which of the following halides does not hydrolyse at room temperature?

The catenation tendency of $C, Si$ and $Ge$ is in the order $Ge < Si < C$. The bond energies (in $kJ \ mol^{-1}$) of $C-C, Si-Si$ and $Ge-Ge$ bonds are respectively:

Explain the following reactions:
$(a)$ Silicon is heated with methyl chloride at high temperature in the presence of copper.
$(b)$ Silicon dioxide is treated with hydrogen fluoride.
$(c)$ $CO$ is heated with $ZnO$.
$(d)$ Hydrated alumina is treated with aqueous $NaOH$ solution.

Hydrolysis of which of the following carbides does not take place?