$Ph-COOH + C_2H_5-^{18}OH \xrightarrow{Conc. H_2SO_4} \text{Major product will be}$

Carboxylic acids react with diazomethane to form

$n$-Propanol on treatment with concentrated $HBr$ gives $P$. The product $P$ on reaction with $KCN$ gave the product $Q$. The product $Q$ on heating with aqueous acidic solution,furnished the product $R$. The product $R$ is

Identify the product of the following reaction:

The silver salt of a carboxylic acid on reaction with $R-X$ gives:

Order of acidity of benzoic acid $(I)$,$4-$methoxybenzoic acid $(II)$,acetic acid $(III)$ and $4-$nitrobenzoic acid $(IV)$ is