Answer:
a. C2H4.
Step-by-step explanation:
Let's look at the balanced equation for C2H4.
C2H4 + 3O2 --> 2CO2 + 2H2O
So 1 mole of this hydrocarbon reacts with 3 moles of oxygen and since 1 mole of one gas occupies the same volume as another gas, the volumes will be in the ratio 1:3. So this is the required hydrocarbon.