The combustion of carbon(II)oxide in oxygen can be represented by equation: 2CO + O 2 → 2CO 2 Calculate the…

Analyze the question: CO burns in O₂ and we need the total volume of gas left at the end, including any unused oxygen and the CO₂ formed. All gases are measured under the same conditions, so Gay-Lussac's law applies: volume ratios equal mole ratios.

Concept: From 2CO + O₂ → 2CO₂, the volume ratio is 2 : 1 : 2.

Solution:

1. 50 cm³ of CO needs half its volume of O₂: 50 ÷ 2 = 25 cm³ of O₂.
2. O₂ supplied = 100 cm³, so O₂ is in excess. The unused O₂ = 100 − 25 = 75 cm³.
3. CO₂ formed: 2 volumes of CO give 2 volumes of CO₂, so 50 cm³ of CO gives 50 cm³ of CO₂.
4. Total volume at the end = unused O₂ + CO₂ = 75 + 50 = 125 cm³.

Answer: B (125 cm³)

Tip: In "volume of the resulting mixture" questions, always check which reactant is limiting and add the leftover excess gas to the product volume. Many students forget the excess and pick 50 cm³ (the CO₂ alone). The question asks for the mixture, so include everything.