A Dibromo derivative (A) on treatment with KCN followed by acid hydrolysis and heating gives a monobasic acid (B) along with liberation of `CO_2`. (B) on heating with liquid ammonia followed by treating with `Br_2"/"KOH` gives (C ) which on treating with `NaNO_3` and HCl at low temprerature followed by oxidation gives a monobasic acid (D) having molecular mass 74. Identify A to D.

Explanation

(a) `underset(1,2-"dibromubutane")(1,2-CH_(3)-CH_(2)-underset(Br)underset(|)(CH)-underset(Br)underset(|)(CH_(2)) overset(KCN) to underset(1,2-"dicyanobutane")(CH_(3)-underset(CN)underset(|)CH - underset(CN)underset(|)(CH_(2)) overset((i) H^(+)//H_(2)O)underset((ii) "Heat") to CO_(2) + underset("Butanoic acid")(CO_(2) + CH_(3) -CH_(2) -CH_(2)-COOH`
2. `underset("Butanoic acid")(CH_(3)-CH_(2)-COOH) overset(liq. NH_(3)) underset(Delta)to underset("Butanamide")(CH_(3)-CH_(2)-CH_(2)-CONH_(2)) overset(Br_(2)//KOH) to underset("1-Aminopropane") (CH_(3)-CH_(2)-CH_(2)-NH_(2))`
3. `underset(1-"Aminopropane")(CH_(3)-CH_(2)-NH_(2)) overset(NaNO_(2)//HCl) underset("Low temperature") to underset(1-"Propanol")(CH_(3)-CH_(2) -OH) overset(K_(2)Cr_(2)O_(7)//H^(+))underset(2(0)) to underset("Propanoic acid")(CH_(3)-CH_(2)-COOH)`
4. Molecular mass of propanoic acid is 74