Permanent magnets are the substances having the property of

Options

A. ferromagnetism at room temperature for long period of time.
B. paramagnetism at room temperature for a long period of time.
C. anti ferromagnetism at room temperature for a long period of time.
D. diamagnetism at room temperature for a long period of time.

Explanation

**Step-by-Step Solution:**

1. **Understanding Permanent Magnets**: Permanent magnets are materials that have the ability to maintain a magnetic field without the need for an external power source. This characteristic is what distinguishes them from temporary magnets, which only exhibit magnetism in the presence of an external magnetic field.

2. **Key Property of Permanent Magnets**: The main property that defines permanent magnets is their ability to retain magnetism after being magnetized. This means that once a permanent magnet is magnetized, it will continue to exhibit magnetic properties even when the external magnetic field is removed.

3. **Residual Magnetism**: The retained magnetic property in permanent magnets is referred to as "residual magnetism." This is the magnetism that remains in the material after it has been magnetized and is a crucial aspect of what makes a magnet "permanent."

4. **Duration of Magnetism**: Permanent magnets are characterized by their ability to hold onto this residual magnetism for a long duration. This long-lasting magnetic property is essential for their applications in various devices and technologies.

5. **Ferromagnetism**: The materials that exhibit permanent magnetism are often ferromagnetic materials. Ferromagnetism is a property of certain materials that allows them to become magnetized and retain that magnetization.

6. **Conclusion**: Therefore, the defining property of permanent magnets is their ability to exhibit ferromagnetism at room temperature for an extended period, even after the removal of an external magnetic field.

**Final Answer**: Permanent magnets are substances that exhibit ferromagnetism at room temperature for a long period of time.

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