The reactions described correspond to the chemical behavior of Phthalic acid (benzene-1,2-dicarboxylic acid).

1. Formation of Anhydride: Dicarboxylic acids with carboxyl groups in proper positions (like 1,2-positions) undergo dehydration on heating to form stable cyclic anhydrides. Phthalic acid loses a molecule of water to form Phthalic anhydride (X). $C_6H_4(COOH)_2 \xrightarrow{\Delta} \text{Phthalic anhydride} + H_2O$
2. Formation of Imide: When treated with ammonia, carboxylic acids form ammonium salts. On strong heating, ammonium phthalate loses water to form Phthalimide (Y). $C_6H_4(COOH)_2 + NH_3 \rightleftharpoons \text{Ammonium phthalate} \xrightarrow{\Delta} \text{Phthalimide} + 2H_2O$

(Note: Succinic acid also shows similar behavior, forming succinic anhydride and succinimide, but Phthalic acid is the specific aromatic example often cited in this context in NEET/NCERT exams).