When a material is used in a magnetic field B,a magnetic moment proportional to B but opposite in direction is induced.The metal is

Options

A. diamagnetic
B. paramagnetic
C. ferromagnetic
D. antimagnetic

Answer

To solve the question, we need to analyze the behavior of different types of magnetic materials when placed in an external magnetic field \( B \). The question states that a magnetic moment is induced that is proportional to \( B \) but in the opposite direction.

### Step-by-Step Solution:

1. **Understanding Magnetic Materials**:
- There are different types of magnetic materials: diamagnetic, paramagnetic, ferromagnetic, and anti-magnetic. Each reacts differently to an external magnetic field.

2. **Analyzing the Given Condition**:
- The question specifies that the induced magnetic moment is proportional to the external magnetic field \( B \) but opposite in direction. This means that when the external magnetic field is applied, the material generates its own magnetic field that opposes the applied field.

3. **Identifying the Type of Material**:
- **Diamagnetic Materials**: These materials are characterized by their tendency to create an induced magnetic field in the opposite direction to an applied magnetic field. They are weakly repelled by the magnetic field.
- **Paramagnetic Materials**: These materials have a small and positive susceptibility to magnetic fields and align with the field, thus not satisfying the condition of being opposite.
- **Ferromagnetic Materials**: These materials have a strong attraction to magnetic fields and also do not satisfy the condition of being opposite.
- **Anti-magnetic Materials**: This term is less commonly used and typically refers to materials that do not exhibit magnetic properties in the presence of a magnetic field.

4. **Conclusion**:
- Since only diamagnetic materials exhibit a magnetic moment that is proportional to the external magnetic field but in the opposite direction, we conclude that the correct answer is **Diamagnetic**.

### Final Answer:
The metal is **Diamagnetic**.