180 ml of hydro carbon having the molecular weight 16 diffuses in 1.5 min.under similar condition time taken by 120 ml of so2 to diffuse is

Graham law  states that the diffusion rate of a gas is inversely proportional to the square root of its molar mass (molecular weight).
 

   

$$\begin{gathered} \frac{\mathrm{Volume} \mathrm{of} \mathrm{hydrocarbon}÷\mathrm{time}}{\mathrm{volume} \mathrm{of} {\mathrm{SO}}_2 ÷\mathrm{time}} =\frac{\sqrt{Mass of hydrocarbon}}{\sqrt{Mass of S{O}_2}} \\ \frac{180÷1.5}{120÷time} =\frac{\sqrt{16}}{\sqrt{64}} \\ \frac{180}{1.5}\times \frac{time}{120} =\frac{4}{8} \\ time =\frac{1}{2} =0.5 min \end{gathered}$$