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.

Explanation

When hydrated alumina is heated with aqueous NaOH solution, sodium tetrahydroxoaluminate (III) is formed.
`Al_2 O_3 . 2 H_2 O(s) + 2NaOH (aq) + H_2 O (I) overset(Delta)to underset("tetrahydroxoaluminate(III)")underset("Sodium")(2Na[Al(OH)_4 ] (aq))`
or `Al_2 O_3. 2H_2 O (s) + 2NaOH (aq) overset(Delta)to underset("Sodium mataaluminate")(2NaAlO_(2) (aq) + 3H_2 O (l))`