11.21. 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.

(a) Silicon is heated with methyl chloride at high temperature in the presence of copper catalyst at 537 K, methyl substituted chlorosilanes MeSiCl₃, Me₂→SiCl₂→, Me₃→SiCl and Me₄→Si are formed.

(b) When silicon dioxide is treated with hydrogen fluoride, first SiF₄→ is formed and then hydro fluorosi