(III) (iii) (P)
(II) (iv) (R)
(I) (i) (S)
(IV) (iii) (Q)
The only CORRECT combination that gives two different carboxylic acids is (III) benzaldehyde (iii) (CH3CO)2O/CH3COOK (P) condensation. It is an example of Perkin condensation. Two isomers cis and trans correspond to two carboxylic acids (Z) and (E) 3-phenylacrylic acid.