A: The speed of a planet is maximum at perihelion .
R : The angular momentum of a planet about centre of sun is conserved .

Options

A. If both Assertion & Reason are true . And the reason is the correct explanation of the assertion , then mark (1)
B. If both Assertion & Reason are true but the reason is not the correct explanation of the assertion , then mark (2)
C. If Assertion is true statement but Reason is false , then mark (3)
D. It will move the same speed , tangentially to the spacecraft

Answer

To solve the question, we need to analyze both the assertion (A) and the reason (R) provided.

### Step-by-Step Solution:

1. **Understanding Perihelion**:
- Perihelion is defined as the point in the orbit of a planet where it is closest to the Sun. At this point, the gravitational force between the planet and the Sun is at its maximum.

**Hint**: Remember that perihelion refers to the closest approach of a planet to the Sun in its elliptical orbit.

2. **Speed of the Planet at Perihelion**:
- According to Kepler's laws of planetary motion, particularly the second law (the law of areas), a line segment joining a planet and the Sun sweeps out equal areas during equal intervals of time.
- Since the area swept out is constant, when the planet is closer to the Sun (at perihelion), it must move faster to sweep out the same area in the same amount of time.

**Hint**: Kepler's second law implies that the speed of a planet varies with its distance from the Sun.

3. **Conservation of Angular Momentum**:
- Angular momentum (L) of a planet in orbit is given by the formula \( L = mvr \), where \( m \) is the mass of the planet, \( v \) is its velocity, and \( r \) is the distance from the Sun.
- In a closed system (like a planet orbiting the Sun), angular momentum is conserved. Therefore, if the distance \( r \) decreases (as the planet approaches the Sun), the velocity \( v \) must increase to keep \( L \) constant.

**Hint**: Angular momentum conservation is a key principle in orbital mechanics.

4. **Conclusion**:
- Since both the assertion (A) that the speed of a planet is maximum at perihelion is correct, and the reason (R) that the angular momentum of a planet about the center of the Sun is conserved is also correct, we conclude that both statements are true.
- Furthermore, the reason provided correctly explains the assertion.

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