$A$ compound $C$ (molecular formula $C_2H_4O_2$) reacts with $Na$ metal to form a compound $R$ and evolves a gas which burns with a pop sound. Compound $C$ on treatment with an alcohol $A$ in the presence of an acid forms a sweet-smelling compound $S$ (molecular formula $C_3H_6O_2$). On addition of $NaOH$ to $C$,it also gives $R$ and water. $S$ on treatment with $NaOH$ solution gives back $R$ and $A$. Identify $C$,$R$,$A$,$S$ and write down the reactions involved.

(A) is Ethanoic acid $(CH_3COOH)$.
$R$ is Sodium acetate $(CH_3COONa)$ and the gas evolved is Hydrogen $(H_2)$.
$A$ is Methanol $(CH_3OH)$.
$S$ is Methyl acetate $(CH_3COOCH_3)$.
$(a)$ Reaction with $Na$ metal:
$2CH_3COOH + 2Na \to 2CH_3COONa + H_2 \uparrow$
$(b)$ Esterification reaction:
$CH_3COOH + CH_3OH \xrightarrow{Conc. H_2SO_4} CH_3COOCH_3 + H_2O$
$(c)$ Reaction with $NaOH$ (Neutralization):
$CH_3COOH + NaOH \to CH_3COONa + H_2O$
$(d)$ Saponification reaction:
$CH_3COOCH_3 + NaOH \to CH_3COONa + CH_3OH$