Assertion (A): It is not necessary that every magnet has one north pole and one south pole.
Reason (R ): It is a basic fact that magnetic poles occur in pairs

Options

A. If both Assertain and Reason are true and Reason is the correct explanation of Assertain
B. If both Assertain and Reason are true but Reason is not correct explantion of Assertain
C. If Assertion is true but Reason is false
D. If Assertion is false but Reason in true.

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: "It is not necessary that every magnet has one north pole and one south pole."
- In magnetism, every magnet is characterized as a dipole, meaning it inherently possesses both a north pole and a south pole. Therefore, the assertion is incorrect.

2. **Understanding the Reason (R)**:
- The reason states: "It is a basic fact that magnetic poles occur in pairs."
- This statement is true because, according to the principles of magnetism, magnetic poles always exist in pairs. If you cut a magnet in half, you will create two smaller magnets, each with its own north and south pole.

3. **Conclusion**:
- Since the assertion (A) is false and the reason (R) is true, we can conclude that the correct relationship between the assertion and the reason is that the assertion is false while the reason is true.

4. **Identifying the Correct Option**:
- Based on the analysis, the correct option is D: "Assertion is false but reason is true."