Ester formation requires specific carbon count from acid and alcohol Steps:

• Esters have general formula C_nH_{2n}O_2 where n = carbons in acid + carbons in alcohol.
• For C4H8O2, n=4, so acid with k carbons pairs with alcohol of 4-k carbons.
• Ethanoic (k=2) pairs with C2 alcohol (ethanol, 1 isomer); propanoic (k=3) with C1 (methanol, 1 isomer); butanoic (k=4) requires C0 alcohol (impossible).
• "One ester" implies single possible product (no alcohol isomers), but both A and B fit; C forms none.

Why C is correct:

• Not applicable; butanoic cannot form C4H8O2 ester.

Why the others are wrong:

• A: Forms one ester (ethyl ethanoate), but question specifies C.
• B: Forms one ester (methyl propanoate), but question specifies C.

Not enough information. Final answer: Not enough information.