C3H8(g)+5O2(g)→3CO2(g)+4H2O(l)
As par above equation 1 mole of porpane reacts with 5 moles of oxygen to form 3 moles of carbon dioxide.
We know that the number of moles is directly proportional to the volume of the gas.
Thus when 15 ml of propane reacts with 75 ml of oxygen, 45 ml of carbon dioxide will be obtained.
The contraction in the volume will be 15+75−45=45ml.
This is possible when the composition of the reacting mixture is either 15ml C3H8 and 85ml O2 or 25ml C3H8 and 75ml O2.
Hence, options A and B are the correct answers.