In the combustion process using excess oxygen, each mole of methane results to 1 mole of co2 while ethane produces 2 moles of Co2. Under same conditions, these can be translated to volume. Hence the total volume absorbed is 10 cm3 + 20 cm3 = 30 cm3.
D. this is the correct answer because the question is showing a comparison of sizes rather than the actual sizes which eliminates B. A and C have no relevance.
