A is wrong. Since propane and oxygen are gases at standard conditions, we can apply Avogadro's law. 10 cm3 of propane requires 50 cm3 of oxygen gas for complete combustion. If the volume is less than 50cm3, we get an incomplete combustion of propane and produce gases such as carbon monoxide. Hence, it is wrong to state that propane CANNOT burn. It will burn but the burning (combustion) is incomplete.
B is wrong. H2O is a liquid based on the state symbol given and hence, we cannot apply Avogadro's law. Option B is correct only if H2O is a GAS.
D is wrong. Assuming that the gaseous reactants are used in stoichiometric amount, 10 cm3 of propane + 50 cm3 of oxygen = initial volume of the gases. After combustion, the only gas left is the carbon dioxide and its volume is only 30 cm3. There is a REDUCTION in volume of 30 cm3 (50 + 10 - 30 = 30). We only consider the volume of gases and not liquid.