Assertion: When distance between bodies is doubled and also mass of each body is also doubled, gravitational force between them remains the same.
Reason: According to Neweton's law gravitational, force is directely proportional to mass of bodies and inversely proportional to square of distance between them.

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 in the context of Newton's law of gravitation.

### Step-by-Step Solution:

1. **Understanding the Gravitational Force Formula**:
The gravitational force \( F \) between two masses \( m_1 \) and \( m_2 \) separated by a distance \( d \) is given by Newton's law of gravitation:
\[ F = \frac{G m_1 m_2}{d^2} \]
where \( G \) is the gravitational constant.

2. **Initial Conditions**:
Let's denote the initial masses as \( m_1 \) and \( m_2 \), and the initial distance as \( d \). The initial gravitational force \( F_1 \) can be expressed as:
\[ F_1 = \frac{G m_1 m_2}{d^2} \]

3. **Doubling the Masses**:
If we double the masses of both bodies, the new masses become \( 2m_1 \) and \( 2m_2 \). The new gravitational force \( F_2 \) can be expressed as:
\[ F_2 = \frac{G (2m_1)(2m_2)}{d^2} = \frac{4G m_1 m_2}{d^2} \]

4. **Doubling the Distance**:
Now, if we also double the distance between the two masses, the new distance becomes \( 2d \). The gravitational force with the new distance can be expressed as:
\[ F_2 = \frac{G (2m_1)(2m_2)}{(2d)^2} = \frac{4G m_1 m_2}{4d^2} = \frac{G m_1 m_2}{d^2} \]

5. **Comparing the Forces**:
From the calculations:
- The initial force \( F_1 = \frac{G m_1 m_2}{d^2} \)
- The new force \( F_2 = \frac{G m_1 m_2}{d^2} \)

We see that \( F_1 = F_2 \). Therefore, the gravitational force remains the same even after doubling the masses and the distance.

6. **Conclusion**:
- The assertion is true: when the distance between the bodies is doubled and the mass of each body is also doubled, the gravitational force between them remains the same.
- The reason is also true: according to Newton's law of gravitation, the force is directly proportional to the masses and inversely proportional to the square of the distance.

### Final Answer:
Both the assertion and the reason are correct, and the reason is the correct explanation for the assertion. Therefore, the answer is:
**Option A: Both assertion and reason are correct, and reason is the correct explanation for assertion.**