Given below are two statements: one is labelled as Assertion A and the other is labelled as Reason R.
Assertion A: Earth has atmosphere whereas moon doesn't have any atmosphere.
Reason R: The escape velocity on moon is very small as compared to that on earth.
In the light of the above statements, choose the correct answer from the options given below:

Assertion A: Earth has atmosphere whereas moon doesn't have any atmosphere.

This is TRUE. Earth has a significant atmosphere while the moon has virtually no atmosphere.

Reason R: The escape velocity on moon is very small as compared to that on earth.

This is TRUE. The escape velocity on the moon is about $$2.38\;\text{km/s}$$, while on Earth it is about $$11.2\;\text{km/s}$$.

The escape velocity determines whether gas molecules can escape the gravitational pull of a celestial body. Since the moon's escape velocity is very low, gas molecules (which have thermal velocities comparable to or exceeding the moon's escape velocity) easily escape from the moon's surface. On Earth, the higher escape velocity retains the atmosphere.

Therefore, R is the correct explanation of A.

The correct answer is Both A and R are correct and R is the correct explanation of A.