Q87 / 200 · NEET 2011 (Screening) · Chemistry

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 $49 \mathrm{u}$. Molecular mass of $B$ will be

Correct answer
A
$12.25 \mathrm{u}$
B
$6.50 \mathrm{u}$
C
$25.00 \mathrm{u}$
D
$50.00 \mathrm{u}$

Solution

$$ \frac{r_A}{r_B}=\sqrt{\frac{M_B}{M_A}} $$ or $\frac{V_A}{t_A} \times \frac{t_B}{V_B}=\sqrt{\frac{M_B}{M_A}}$ or $\quad \frac{10}{20}=\sqrt{\frac{M_B}{49}}$ or $\quad \frac{1}{4}=\frac{M_B}{49}$ $\therefore \quad M_B=\frac{49}{4}=12.25 \mathrm{u}$.

Hence, the correct answer is option: 'A'.

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