At $300\;K$ and $1\;atm, 15\; mL$ of a gaseous hydrocarbon requires $375\; mL$ air containing $20\%$ $O_2$ by volume for complete combustion. After combustion the gases occupy $330\; mL$. Assuming that the water formed is in liquid form and the volumes were measured at the same temperature and pressure, the formula of the hydrocarbon is

Question

$\begin{array}{1 1} (1)C_3H_6 \\ (2)C_3H_3 \\ (3)C_4H_8 \\ (4) C_4H_{10} \end{array}$