Question

Moon has no atmosphere because

• A. it is a satellite of earth.
• B. it does not have population.
• C. it is colder than earth.
• D. r.m.s velocity of all the gases is more than the escape velocity from its surface.

Answer 1

The correct option is D r.m.s velocity of all the gases is more than the escape velocity from its surface.

r.m.s. velocity or root mean square velocity is the measure of the speed of particles in a gas. It is defined as $V_{rms}=\sqrt{\frac{3RT}{M}}$, where $V_{rms}$ is the root mean square of the speed in meters per second, Mm is the molar mass of the gas in kilograms per mole, R is the molar gas constant, and T is the temperature in Kelvin.
Since r.m.s velocity of all the gases is more than the escape velocity from its surface, all the gases escape the surfce of moon. That is why moon does not have any atmosphere.