Which carboxylic acid has the formula C3H6O2?

The carboxylic acid with the formula C3H6O2 is propanoic acid. This is because carboxylic acids are characterized by the presence of the carboxyl group (-COOH). To determine the correct formula for each of the provided acids, we can look at their molecular formulas:

• Methanoic acid (C1H2O2) contains one carbon atom.
• Ethanoic acid (C2H4O2) has two carbon atoms.
• Butanoic acid (C4H8O2) consists of four carbon atoms.

Propanoic acid, on the other hand, has three carbon atoms, matching the formula C3H6O2. In general, each carboxylic acid differs in the number of carbon atoms linked to the carboxyl group, which directly affects their molecular formula. Thus, propanoic acid, with its specific three-carbon structure, is the correct answer.