Answer: A. Complete combustion: \(\text{CH}_4 + 2\text{O}_2 \rightarrow \text{CO}_2 + 2\text{H}_2\text{O}\). 100 cm³ of \(\text{CH}_4\) needs 200 cm³ of \(\text{O}_2\), but only 150 cm³ is available — \(\text{O}_2\) is the limiting reagent. The combustion is incomplete: some carbon ends up as CO instead of \(\text{CO}_2\), and some \(\text{CH}_4\) may be left unburnt.
On cooling to room temperature, water vapour condenses to liquid and is not in the gas mixture. The possible gaseous products are: unreacted \(\text{CH}_4\), partly-burnt \(\text{CO}\), fully-burnt \(\text{CO}_2\) — matching option A.
Option B includes \(\text{H}_2\text{O}\) (condensed at room temp, so it shouldn't be in the gas list). Options C and D include \(\text{H}_2\) and \(\text{O}_2\), neither of which are produced — methane combustion doesn't make hydrogen, and the limiting reagent \(\text{O}_2\) is fully consumed.
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