Question

What is the approximate molecular mass of dry air containing 78% $N_2$ and 22% $O_2$?

• A. 28.88
• B. 27
• C. 30
• D. 34

Answer 1

The correct option is A 28.88

The molecular mass of dry air is given by-

$=\frac{[\text{Molecular mass of}{N}_2\times \text{Percentage of}{N}_2]+[\text{Molecular mass of}{O}_2\times \text{Percentage of}{O}_2]}{\text{Percentage of}{N}_2+\text{Percentage of}{O}_2}$

$=\frac{[\text{28}\times \text{78}]+[\text{32}\times \text{22}]}{\text{78}+\text{22}}$

$=\text{28.88 g/mol}$

Hence, option $A$ is correct.