Assertion : Ferro magnetic substances become paramagnetic above Curie temp.
Reason : Domains are destroyed at high temp.

Options

A. If both assertion and reason are true and reason is the correct explanation of assertion
B. If both assertion and reason are true but reason is not the correct explanation of assertion
C. If assertion is true but reasonb is false
D. If both assertion and reason are false.

Explanation

To solve the question, we need to analyze both the assertion and the reason provided.

**Assertion:** Ferro magnetic substances become paramagnetic above Curie temperature.

**Reason:** Domains are destroyed at high temperature.

### Step-by-Step Solution:

1. **Understanding Ferromagnetism:**
- Ferromagnetic materials have regions called magnetic domains, where the magnetic moments of atoms are aligned in the same direction. This alignment leads to a net magnetic moment in the material.

2. **Curie Temperature:**
- The Curie temperature (Tc) is the temperature above which a ferromagnetic material loses its ferromagnetic properties and becomes paramagnetic. This is a critical point in the behavior of ferromagnetic materials.

3. **Effect of Temperature on Magnetic Domains:**
- As the temperature of a ferromagnetic material increases and approaches the Curie temperature, thermal energy disrupts the alignment of the magnetic domains. At the Curie temperature, the thermal agitation is sufficient to overcome the magnetic interactions that keep the domains aligned.

4. **Transition to Paramagnetism:**
- Above the Curie temperature, the magnetic domains are no longer aligned, and the material behaves as a paramagnet. In a paramagnetic state, the material will have a weak and temporary magnetic response to an external magnetic field, but it will not retain any magnetization in the absence of the field.

5. **Conclusion:**
- Therefore, the assertion that ferromagnetic substances become paramagnetic above the Curie temperature is correct. The reason provided, stating that domains are destroyed at high temperatures, is also correct as it explains why the transition occurs.

### Final Answer:
Both the assertion and the reason are correct, and the reason correctly explains the assertion.

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