Explanation

(a)
Only acidic compounds such as acetic acid, phenol and alcohol react with sodium metal. Ether is not acidic in nature, hence it does react with sodium metal.
$2CH_{3}CH_{2}OH + 2Na \rightarrow 2CH_{3}CH_{2}ONa + H_{2}$
Ethanol sodium ethoxide
$2CH_{3}COOH + 2Na \rightarrow 2CH_{3}COONa + H_{2}$
Acetic acid sodium acetate
$2C_{6}H_{5}OH + 2Na \rightarrow 2C_{6}H_{5}ONa + H_{2}$
Phenol sodium
phenoxide
$CH_{3} - O - CH_{3} + Na \rightarrow$ No reaction