250CC. of methane diffuses through a porous pot in 30S. Under same conditions the volume of helium diffused in 60S will be

CH₄                                He

V₁ = 250CC.                  V₂ = ?

t₁ = 30 sec                    t₂ =60 sec

M₁ =16                           M₂ = 4

$$\begin{gathered} \sqrt{\frac{{\mathrm{M}}_2}{{\mathrm{M}}_1}} = \frac{V_1\times t_2}{V_2\times t_1} \\ \sqrt{\frac{4}{16}}=\frac{250\times 60}{x \times 30} \\ \sqrt{\frac{1}{4}}=\frac{500}{x} \\ \frac{1}{2}=\frac{500}{x} \\ x =\frac{500\times 2}{1}=1000\mathrm{cc} \end{gathered}$$