Question

Oxygen and nitrogen are present in a mixture in the ratio of $1:4$. Calculate the ratio of their number of molecules in the mixture.

• A. $32:7$
• B. $7:32$
• C. $16:28$
• D. $8:14$

Answer 1

The correct option is B $7:32$

Let wt. of given mixture = $W\text{g}$
Amount of $oxygen$ in mixture = $\frac{W\times 1}{5}=\frac{W}{5}\text{g}$
Amount of $nitrogen$ in mixture = $\frac{W\times 4}{5}=\frac{4W}{5}\text{g}$
Moles of $O_2=\frac{W}{5\times 32}$
Molecules of $O_2$$=\frac{W}{5\times 32}\times N_a$
Moles of $N_2=\frac{4W}{5\times 28}$
Molecules of $N_2$$=\frac{4W}{5\times 28}\times N_a$
Ratio of molecules of $O_2$ to $N_2$
$\frac{1}{32}:\frac{1}{7}=7:32$