A : If angular momentum of an object is constant about a point then net torque on it about that point is zero.
R : Torque is equal to the rate of change of angular momentum.

Options

A. If both Assertion & Reason are true and the reason is the correct explanation of the assertion,
B. If both Assertion & Reason are true but the reason is not the correct explanation of the assertion,
C. If Assertion is true statement but Reason is false,
D. If both Assertion and Reason are false statements,

Answer

To solve the given problem, we need to analyze the statements A and R regarding angular momentum and torque.

### Step-by-Step Solution:

1. **Understanding Angular Momentum**:
- Angular momentum (L) of an object about a point is defined as \( L = r \times p \), where \( r \) is the position vector from the point to the object, and \( p \) is the linear momentum of the object.
- If the angular momentum is constant about a point, it means that \( \frac{dL}{dt} = 0 \).

2. **Relating Torque to Angular Momentum**:
- Torque (\( \tau \)) is defined as the rate of change of angular momentum:
\[ \tau = \frac{dL}{dt} \]
- If the angular momentum is constant, then its rate of change is zero, which implies:
\[ \tau = 0 \]
- Therefore, if the angular momentum is constant about a point, the net torque about that point must also be zero.

3. **Evaluating Statement A**:
- Statement A claims: "If angular momentum of an object is constant about a point, then net torque on it about that point is zero."
- Based on our analysis, this statement is **true**.

4. **Evaluating Statement R**:
- Statement R claims: "Torque is equal to the rate of change of angular momentum."
- This is a direct definition of torque, which we have already established as \( \tau = \frac{dL}{dt} \).
- Therefore, this statement is also **true**.

5. **Conclusion**:
- Both statements A and R are true.

### Final Answer:
- Statement A is true, and Statement R is true.