Assertion : Moon has no atmosphere.
Reason : The escape velocity for moon is less than that for earth.

Options

A. If both assertion and reason are true and reason is the correct explanation of assertion
B. If both assertion and reason are truebut reason is not the correct explanation of assertion
C. If assertion is true but reason is false
D. If both assertion and reason are false.

Explanation

To solve the question, we need to analyze the assertion and the reason provided.

### Step 1: Analyze the Assertion
The assertion states that "Moon has no atmosphere." This statement is indeed correct. The Moon has a very thin exosphere, which is not substantial enough to be considered an atmosphere.

**Hint:** Consider what constitutes an atmosphere and the conditions on the Moon.

### Step 2: Analyze the Reason
The reason states that "The escape velocity for the Moon is less than that for Earth." This statement is also correct. The escape velocity is the minimum speed needed for an object to break free from the gravitational pull of a celestial body. The escape velocity for the Moon is approximately 2.38 km/s, while for Earth, it is about 11.2 km/s.

**Hint:** Recall the formula for escape velocity and how it relates to the mass and radius of a celestial body.

### Step 3: Relate the Assertion and Reason
Now, we need to determine if the reason correctly explains the assertion. The escape velocity being lower on the Moon means that the gravitational pull is weaker, which allows gas molecules to escape more easily. Since the thermal velocities of gas molecules can exceed the escape velocity, they can escape into space, leading to the absence of a significant atmosphere on the Moon.

**Hint:** Think about how escape velocity and thermal velocity of gas molecules interact.

### Step 4: Conclusion
Both the assertion and reason are correct, and the reason provides a valid explanation for the assertion. Therefore, we conclude that the correct answer to the question is that both statements are true, and the reason is a correct explanation of the assertion.

**Final Answer:** Both the assertion and reason are correct, and the reason is the correct explanation of the assertion.