Silicon is an important component of which of the following?

Which pair of elements can form multiple bonds with itself and oxygen?

Superphosphate is a mixture of

Assertion $(A): [SiF_6]^{2-}$ is formed but $[SiCl_6]^{2-}$ is not.
Reason $(R):$ Electronegativity $(EN)$ of $F$ is higher than $EN$ of $Cl$.

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.

Which gas is used in aerated water?