Assertion:A disc-shaped mahnet is leviated above a superconductiong material that has been cooled by liquid nitrogen.
Reason:Superconductors repal a magnet.

Options

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

### Step-by-Step Solution:

1. **Understanding the Assertion**:
- The assertion states that a disc-shaped magnet is levitated above a superconducting material that has been cooled by liquid nitrogen.
- This is possible because superconductors exhibit a phenomenon known as the Meissner effect when they are below their critical temperature.

2. **Understanding the Reason**:
- The reason given is that superconductors repel magnets.
- This is true due to the Meissner effect, which causes a superconductor to expel magnetic fields and create an opposing magnetic field when a magnet is brought close to it.

3. **Critical Temperature**:
- Superconductors only exhibit their unique properties below a certain critical temperature. Liquid nitrogen is often used to cool materials to achieve this state.

4. **Induced Magnetic Field**:
- When the disc-shaped magnet is placed above the cooled superconductor, the superconductor will induce a magnetic field that is equal in magnitude but opposite in direction to the magnetic field of the disc-shaped magnet.
- This induced magnetic field cancels the applied magnetic field within the superconductor.

5. **Resulting Forces**:
- The equal and opposite magnetic fields create a repulsive force between the magnet and the superconductor.
- This repulsive force is strong enough to levitate the magnet above the superconductor.

6. **Conclusion**:
- Since both the assertion and the reason are correct, and the reason correctly explains the assertion, we conclude that the answer to the question is that both the assertion and reason are true, and the reason is the correct explanation for the assertion.

### Final Answer:
Both the assertion and the reason are correct, and the reason is the correct explanation of the assertion.

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