Which among the following compounds is obtained when ethanenitrile is acid hydrolysed?

Which of the following gives benzoic acid on oxidation?

Which of the following would be the best synthesis of $2,2-$dimethylpropanoic acid?

The correct set$(s)$ of reactions to synthesize benzoic acid starting from benzene is/are:

Toluene on reaction with reagent $A$ gives $X$. This $(X)$ forms $2,4-$dinitrophenylhydrazone and reduces ammonical silver nitrate solution. Reaction of toluene with another reagent $B$ forms $Y$,which dissolves in $NaHCO_3$ with evolution of $CO_2$. What are $A$ and $B$ respectively?

What will be the final product of the following reaction sequence?
$CH \equiv CH$ $\xrightarrow{CH_3MgBr}$ $\xrightarrow{CO_2/H_3O^+}$ $\xrightarrow{HgSO_4/H_2SO_4}$ $\xrightarrow{Ag_2O, \Delta} ?$