Stoichiometric combustion with water condensation Steps:

• 100 cm³ air contains 20 cm³ O₂ (20%) and 80 cm³ N₂.
• 10 cm³ CH₄ requires 20 cm³ O₂ for complete combustion per CH₄ + 2O₂ → CO₂ + 2H₂O(l).
• Reaction produces 10 cm³ CO₂ (1:1 volume ratio with CH₄); all O₂ consumed, no excess.
• After cooling, H₂O is liquid; gaseous mixture is 10 cm³ CO₂ + 80 cm³ N₂. Why B is correct:
• Lists only the remaining gases (CO₂ from reaction, inert N₂) based on Avogadro's law for gas volumes at RTP. Why the others are wrong:
• A: Includes excess O₂ (none present) and steam (H₂O condenses to liquid).
• C: Identical to B but listed as distractor; assumes no distinction.
• D: Identical to B but listed as distractor; assumes no distinction.

Final answer: B