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.

(N/A) When silicon is heated with methyl chloride at a high temperature of $573 \ K$ in the presence of copper catalyst,a mixture of methyl-substituted chlorosilanes like $MeSiCl_3$,$Me_2SiCl_2$,$Me_3SiCl$,and $Me_4Si$ is formed.
$(b)$ Silicon dioxide reacts with hydrogen fluoride to form silicon tetrafluoride,which further reacts with excess $HF$ to form hydrofluorosilicic acid:
$SiO_2 + 4HF \rightarrow SiF_4 + 2H_2O$
$SiF_4 + 2HF \rightarrow H_2SiF_6$
$(c)$ Carbon monoxide acts as a reducing agent and reduces zinc oxide to zinc metal upon heating:
$CO + ZnO \xrightarrow{\Delta} CO_2 + Zn$
$(d)$ Hydrated alumina dissolves in aqueous $NaOH$ solution to form sodium meta-aluminate:
$Al_2O_3 \cdot 2H_2O + 2NaOH \rightarrow 2NaAlO_2 + 3H_2O$