Convert 1-chlorobutane (A) to valeric acid `(B)`.

Explanation

(a) Proceed reverse :
(i) `(-COOH)` can be obtained either by the oxidation of `(-CHO)` group or by `(CH_2 OH)` group.
(ii) `(-COOH)` can be obtained by the oxidative cleavage of `(C=C)` bond or `(C -= C)` bond.
(iii) `(-COOH)` can be obtained by the haloform reaction of `(Me-overset(O)overset(||)(C)-)` group.
The compounds are :

(b) Since in the conversion of `(A)` to `(B)`, there is an increase of an `C` atom, thus step-up method can be obtained (i) from Grignard reagent and (ii) ny nitrile method.
(i) From Grignard reagent :

(ii) By nitrile method :
`(A) overset(CN^(Ө))rarr Me(CH_2)_3 CN overset (H_3 O^(oplus))rarr Me (CH_2)_3 COOH + overset (oplus) NH_4`
( c) Adipic acid is a dibasic acid of six `C` atoms, and benzene also has six `C` atoms. So, first conversion to cyclohexene and then oxidation of `(C=C)` would give adipic acid.

(d) (i)