Ethylene C2H2 reacts with Oxygen according to the equation below. what volume of Oxygen (in dm3) reacts with 0.40 dm3 of C2H2?

2C2H2 (g) 5O2 (g) → 4 CO2 (g) 2H2O (g) ? (1) 0.4 (3) 0.80 (2) 1.0 (4) 2.0

The answer is (2) 1.0 dm3. In a balanced equation, the ratio of the mole number of the compounds is equal to the coefficients. And the ratio of volume of gas is equal to the mole number under same condition. So the answer is 1.0 mol.