Identify the products.

P: Hot alkaline $KMn{O}_4$ oxidises only the side chain with benzylic hydrogens. The ethyl group is oxidised to $-COOH$ while the $tert$-butyl group (no benzylic H) is left untouched. After acidic workup, P is 4-tert-butylbenzoic acid, a monocarboxylic acid.

Q: Aqueous $NaOH$ hydrolyses both the acid chloride and the methyl ester at the meta positions. Acidic workup gives benzene-1,3-dicarboxylic acid (isophthalic acid).

R: Acid hydrolysis of the methyl ester gives a $\beta$-keto acid that decarboxylates on heating to leave a methyl ketone with the spectator $-COOH$. Oxidation by $H_{2}Cr{O}_4$ converts the methyl ketone to a second carboxyl group, again furnishing isophthalic acid.

S: The bromoarene forms a Grignard that adds to $C{O}_2$ to give a benzoic acid bearing $-CN$ and the protected aldehyde. Tollens reagent (ammoniacal $AgN{O}_3$) hydrolyses the cyclic acetal to the aldehyde and simultaneously oxidises the aldehyde to a carboxylic acid; the nitrile also hydrolyses to a carboxylic acid under prolonged aqueous conditions. The final product S is a tricarboxylic aromatic acid (no aldehyde remaining).

Evaluate each option.

(A) Wrong. Dacron uses terephthalic acid (1,4) with ethylene glycol; glyptal uses phthalic acid (1,2) with glycerol. P is 4-tert-butylbenzoic acid and Q is isophthalic acid (1,3); neither is the monomer of dacron or glyptal.

(B) Wrong. P is a monocarboxylic acid, so the claim that P, Q, R are all dicarboxylic acids fails.

(C) Correct. Both Q and R are isophthalic acid.

(D) Correct. R (isophthalic acid) has no $\alpha$-hydrogens, so no aldol condensation is possible. S, having no aldehyde group, does not undergo Cannizzaro.

Correct options: (C) and (D).