Question

Which of the following gas molecule has the longest mean free path at the same pressure and temperature?

• A. ${\mathrm{Cl}}_2$
• B. ${\mathrm{H}}_2$
• C. ${\mathrm{N}}_2$
• D. ${\mathrm{O}}_2$

Answer 1

The correct option is B

${\mathrm{H}}_2$

Explanation for correct option:

B. ${\mathrm{H}}_2$

Mean free path:

• “The mean free path is the average distance traveled by a moving particle between successive collisions.”
• The mean free path is inversely proportional to molar mass. So, the smaller the molar mass, the higher the mean free path.
• Hydrogen$\left(1\right)$ has a minimum molar mass in comparison to oxygen$\left(16\right)$, nitrogen$\left(14\right)$ as well as chlorine$\left(35.5\right)$. Thus, it will have the longest mean free path.

Explanation for incorrect options:

Hydrogen will have the longest mean free path. Thus, options A, C, and D are incorrect.

Hence, the correct option is B i.e. ${\mathrm{H}}_2$.