Sodium bicarbonate is a weak base whose conjugate acid, carbonic acid, has a pK_a of about 6.4. A compound can liberate carbon dioxide from bicarbonate only if it is more acidic than carbonic acid. Carboxylic acids have pK_a values near 4 to 5, making them strong enough to protonate bicarbonate and release carbon dioxide as brisk effervescence. Phenols, with pK_a values near 10, are far weaker acids and cannot displace carbonic acid, so they give no effervescence. This difference makes the bicarbonate test a clean way to distinguish the two. Option B is wrong because the phenol does not react, so the gas evolution is not equal. Option C reverses the true acid strengths, incorrectly attributing reactivity to the phenol. Option D is incorrect because the carboxylic acid clearly does react. This relative-acidity reasoning is exactly the NCERT criterion used to order carboxylic acids, carbonic acid, and phenols. Plausibility check: only an acid stronger than carbonic acid can drive the equilibrium toward carbon dioxide release, consistent with the carboxylic acid being the lower-pK_a species.