Question

The ratio of masses of oxygen and nitrogen in a particular gaseous mixture is $1:4$. Their ratio of number of molecules is:

• A. $1:4$
• B. $7:32$
• C. $1:8$
• D. $3:16$

Answer 1

The correct option is B $7:32$

$\text{Number of moles of}{O}_2=\frac{Givenmass}{Molarmass}=\frac{w}{32}$
$\text{Number of moles of}{N}_2=\frac{Givenmass}{Molarmass}=\frac{4w}{28}=\frac{w}{7}$
As ratio of molecules would also equal to ratio of their moles:
$\therefore \text{Ratio of their molecules}=\frac{w}{32}:\frac{w}{7}=7:32$