Question

A certain gas takes three times as long to effuse out as helium. Its molecular mass will be:

• A. 36 u
• B. 64 u
• C. 9 u
• D. 27 u

Answer 1

Answer: (A)

36 u

Answer 2

$\frac{r_{1}}{r_{2}} = \sqrt{\frac{M_{w_2}}{M_{w_1}}}$
$\frac{V_{1}}{t_{1}} \times\frac{t_{2}}{V_{2}} = \sqrt{\frac{M_{W_2}}{M_{W_1}}}$
volume is same
$\frac{3}{1} = \sqrt{\frac{M_{W_2}}{4}}$
$9 = \frac{M_{W_2}}{4} \therefore M_{W_2} = 36$