The correct option is **B. Iron**. ### Detailed Explanation **1. Understanding Ferromagnetism:** Ferromagnetic materials are substances that can be magnetized; they have a strong magnetic response to an external magnetic field. The key characteristic of ferromagnetic materials is their ability to retain magnetization even after the external magnetic field is removed. This property is due to the alignment of magnetic domains within the material. **2. Magnetic Domains:** In ferromagnetic materials, such as iron, the atoms have magnetic moments that can align in the same direction. When an external magnetic field is applied, these magnetic moments align, and the material becomes magnetized. Once the external field is removed, the magnetic moments may remain aligned, allowing the material to retain its magnetization. This phenomenon is known as hysteresis. **3. Why Iron is Ferromagnetic:** Iron is a classic example of a ferromagnetic material. It has a high permeability, meaning it can easily become magnetized, and it has a significant ability to retain that magnetization. This property is utilized in various applications, such as in the cores of transformers and in permanent magnets. ### Analysis of Other Options **A. Copper:** - **Why it's incorrect:** Copper is a non-magnetic material. It does not exhibit ferromagnetism, and it cannot be magnetized in the same way that iron can. When exposed to a magnetic field, copper does not retain any magnetization once the field is removed. Instead, it is a good conductor of electricity and is often used in electrical wiring. **C. Aluminum:** - **Why it's incorrect:** Aluminum is also a non-ferromagnetic material. While it can be weakly magnetized (it exhibits paramagnetism), it does not retain magnetization after the external magnetic field is removed. Its magnetic properties are much weaker compared to ferromagnetic materials like iron. **D. Wood:** - **Why it's incorrect:** Wood is a non-magnetic material and does not exhibit any magnetic properties. It cannot be magnetized and does not respond to magnetic fields. Therefore, it cannot retain magnetization. ### Summary of Key Points - **Ferromagnetic materials** can be magnetized and retain magnetization after the external magnetic field is removed. - **Iron** is a prime example of a ferromagnetic material due to its ability to align magnetic domains and retain magnetization. - **Copper, aluminum, and wood** do not exhibit ferromagnetism and cannot retain magnetization after the removal of an external magnetic field. ### Revision Summary - Ferromagnetic materials retain magnetization after an external field is removed. - Iron is a classic ferromagnetic material with strong magnetic properties. - Copper and aluminum are non-ferromagnetic; they do not retain magnetization. - Wood is also non-magnetic and does not respond to magnetic fields.