Answer: C (the ester has more oxygen atoms than the alcohol). Esterification is \(\text{R-OH} + \text{R'-COOH} \rightarrow \text{R'-CO-O-R} + \text{H}_2\text{O}\).
Counting oxygen atoms: the alcohol R-OH has 1; the carboxylic acid R'-COOH has 2; the ester R'-CO-O-R has 2.
So the ester has the same number of oxygen atoms as the carboxylic acid (which rules out A and D) and more than the alcohol (2 against 1, which rules out B). Only C is correct. Answer C.
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