A conductor behaves as a superconductor

Options

A. Above critcal temperature
B. At critical temperature
C. At `100^(@)C`
D. At boiling point of that metal

Answer

To solve the question "A conductor behaves as a superconductor," we need to understand the concept of superconductivity and the conditions under which a conductor becomes a superconductor.

### Step-by-Step Solution:

1. **Understanding Superconductivity**:
- Superconductivity is a phenomenon where a conductor exhibits zero electrical resistance and the expulsion of magnetic fields when cooled below a certain critical temperature (Tc).

2. **Identifying Critical Temperature**:
- Each superconducting material has a specific critical temperature (Tc) below which it transitions into the superconducting state. For some metals, this temperature can be as low as 77 Kelvin.

3. **Behavior of Resistance with Temperature**:
- As the temperature of a conductor decreases, its electrical resistance typically decreases as well. This is due to the positive temperature coefficient of resistance in most conductors.

4. **Reaching Critical Temperature**:
- When the temperature reaches the critical temperature (Tc), the resistance of the conductor drops abruptly to zero. This is the defining characteristic of superconductivity.

5. **Conclusion**:
- Therefore, a conductor behaves as a superconductor at the critical temperature (Tc). Above this temperature, the conductor will still have some resistance and will not exhibit superconducting properties.

### Final Answer:
A conductor behaves as a superconductor at the critical temperature.