Answer: B. Compute H:C ratio for each compound:
Ethanoic acid \(\text{CH}_3\text{COOH} = \text{C}_2\text{H}_4\text{O}_2\) → H:C = 4:2 = 2:1 ✓
Ethane \(\text{C}_2\text{H}_6\) → H:C = 6:2 = 3:1 ✗
Ethene \(\text{C}_2\text{H}_4\) → H:C = 4:2 = 2:1 ✓
Ethanol \(\text{C}_2\text{H}_5\text{OH} = \text{C}_2\text{H}_6\text{O}\) → H:C = 6:2 = 3:1 ✗
The two compounds with H:C = 2:1 are ethanoic acid and ethene — option B.
Note that ethanoic acid and ethene have the same H:C ratio despite being chemically very different (one a carboxylic acid, one an alkene) — H:C ratio alone doesn't determine functional group.
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