Question

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

• A. 12.25 u
• B. 6.50 u
• C. 25.00 u
• D. 50.00 u

Answer 1

Answer: (A)

12.25 u

Answer 2

$\frac{ r _{ A }}{ r _{ B }}=\sqrt{\frac{ M _{ B }}{ M _{ A }}}$ $\Rightarrow \frac{ v _{ A }}{ t _{ A }} \times \frac{ t _{ B }}{ v _{ B }}=\sqrt{\frac{ M _{ B }}{ M _{ A }}}$ $\Rightarrow \frac{10}{20}=\sqrt{\frac{ M _{ B }}{49}}$ $\Rightarrow \frac{1}{4}=\frac{ M _{ B }}{49}$ $\therefore M _{ B }=\frac{49}{4}=12.25$