Carboxylic acids react with Mg, aq NaOH, and EtOH Steps:

• Identify functional groups that chemically react with all three reagents: Mg (active metal), aq NaOH (base), and EtOH (alcohol).
• -COOH reacts with Mg to form salt and H₂ (2RCOOH + Mg → (RCOO)₂Mg + H₂), with aq NaOH to form carboxylate (RCOOH + NaOH → RCOONa + H₂O), and with EtOH to form ester (RCOOH + CH₃CH₂OH → RCOOCH₂CH₃ + H₂O, acid-catalyzed).
• Other groups fail to react with at least one reagent, eliminating them.
• Compound T must contain -COOH to exhibit all reactions.

Why C is correct:

• Carboxylic acids are sufficiently acidic (pKa ~4-5) to liberate H₂ from Mg, neutralize NaOH per acid-base reaction, and undergo Fischer esterification with EtOH.

Why the others are wrong:

• A. Alcohols (pKa ~15-18) do not react with Mg or aq NaOH.
• B. Terminal alkynes (pKa ~25) do not react with aq NaOH or Mg.
• D. Esters hydrolyze with aq NaOH but inert to Mg and EtOH.

Final answer: C