A compound C (molecular formula, `C_(2)H_(4)O_(2)`) reacts with Na metal to form a compounds 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 form a sweet smelling compound S (molecular formula, `C_(3)H_(6)O_(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.

Explanation

(i) Since, compounds `C(M.F.C_(2)H_(4)O_(2))` contains two oxygen atoms, therefore most probably it may be carboxylic acid, i.e., ethanoic acid `(CH_(3)COOH)`
(ii) Since, an acid, i.e., ethanoic acid reacts with a base, i.e., Na metal to evolve a gas which burns with a pop sounds along with formation of compound (r), therefore, R must be a salt, i.e., sodium ethanoate and the gas which burns with a pop sound must be `H_(2)` gas.
`underset("Ethanoic")(2CH_(3))underset((M.F. C_(2)H_(4)O_(2)))underset("acid(C)")overset(O)overset(||)(-C-)OH+underset("Sodium")(2Na)tounderset("ethanoate(R)")underset("Sodium")(2CH_(3))-overset(O)overset(||)C-ONa+underset("pop sound")underset("Burns with a")(H_(2))`
`H_(2)` gas burns with 'pop' sound.
Compound R is sodium ethanoate. This is also suppored by observation that when ethanoic acid reacts with NaOH, it gives R, is sodium ethanoate and water.
`underset((C))underset("Ethanoic acid")(CH_(3)-overset(O)overset(||)C-OH)+NaOHtounderset((R))underset("Sodium ethanoate")(CH_(3)-overset(O)overset(||)C-ONa+)H_(2)O`
`CH_(3)COOH+CH_(3)OHoverset(Conc.H_(2)SO_(4))toCH_(3)COOCH_(3)+H_(2)Ounderset(S)((C_(3)H_(6)O_(2)))`
Since, compound C on treatment with an alcohol A in presence of acid forms a sweet smelling compound `S(M.F. C_(3)H_(6)O_(2))`, therefore, S is methyl ethanoate (ester).
Since, ester S has three carbon atoms and the acid C has two carbon atoms, therefor alcohol A must contain one C atom, i.e., A is methanol.
`underset((S))underset("Methl ethanoate")(CH_(3)COOCH_(3))+NaOHtoCH_(3)underset(R)(COONa)+underset(A)(CH_(3)OH)`
Thus, `C=CH_(3)COOH`
`R=CH_(3)COONa`
`A=CH_(3)OH`
`S=CH_(3)COOCH_(3)`