(A) : A current carrying circular loop, free to turn, when placed in an external magnetic field, orients its plane normal to field.
(R) : The potential energy of the system is minimum at stable equilibrium position.

Options

A. Both 'A' and 'R' are true and 'R' is the correct explanation of 'A'.
B. Both 'A' and 'R' are true and 'R' is not the correct explanation of 'A'
C. 'A' is true and 'R' is false
D. 'A' is false and 'R' is false

Answer

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

### Step-by-Step Solution:

1. **Understanding the Assertion (A)**:
- The assertion states that a current-carrying circular loop, when placed in an external magnetic field, will orient its plane normal (perpendicular) to the magnetic field.
- This happens because the magnetic moment of the loop tends to align with the magnetic field to minimize the potential energy of the system.

2. **Understanding the Reason (R)**:
- The reason states that the potential energy of the system is minimum at the stable equilibrium position.
- In physics, systems tend to move towards configurations that minimize their potential energy. For a magnetic moment \( \mathbf{m} \) in a magnetic field \( \mathbf{B} \), the potential energy \( U \) is given by:
\[ U = -\mathbf{m} \cdot \mathbf{B} = -mB \cos(\theta) \]
- Here, \( \theta \) is the angle between the magnetic moment and the magnetic field.

3. **Analyzing the Minimum Potential Energy**:
- The potential energy is minimized when \( \cos(\theta) \) is maximized, which occurs when \( \theta = 0^\circ \) (i.e., when \( \mathbf{m} \) is parallel to \( \mathbf{B} \)).
- When the loop is oriented such that its area vector is perpendicular to the magnetic field, it achieves this stable equilibrium.

4. **Conclusion**:
- Since both the assertion (A) and the reason (R) are true, and the reason correctly explains the assertion, we can conclude that both statements are valid.

### Final Answer:
- Both (A) and (R) are true, and (R) is the correct explanation for (A).