States of Matter - Result Question 8
####8. Two gases $A$ and $B$ having the same volume diffuse through a porous partition in 20 and 10 seconds respectively. The molecular mass of $A$ is $49 u$. Molecular mass of $B$ will be :
[2011]
(a) $50.00 u$
(b) $12.25 u$
(c) $6.50 u$
(d) $25.00 u$
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Solution:
(b) $\frac{r_A}{r_B}=\sqrt{\frac{M_B}{M_A}}$
$\frac{\frac{V}{20}}{\frac{V}{10}}=\sqrt{\frac{M_B}{49}} \Rightarrow \frac{1}{2}=\sqrt{\frac{M_B}{49}}$
$M_B=\frac{1}{4} \times 49=12.25 u$
