The correct option is **D. retains magnetism more than iron**. ### Detailed Explanation: 1. **Understanding Permanent Magnets**: - Permanent magnets are materials that can maintain a magnetic field without the need for an external power source. The ability of a material to retain its magnetism after being magnetized is crucial for its use in permanent magnets. 2. **Magnetic Properties of Steel vs. Iron**: - **Steel** is an alloy primarily made of iron, with a small percentage of carbon and other elements. The presence of these additional elements in steel enhances its magnetic properties, particularly its ability to retain magnetism. - **Iron**, while it can be magnetized easily, tends to lose its magnetism more quickly than steel when the external magnetic field is removed. This is due to its lower coercivity, which is a measure of a material's ability to withstand demagnetization. 3. **Coercivity**: - Coercivity is a critical factor in determining how well a material can retain its magnetism. Steel has a higher coercivity compared to pure iron, meaning it is more resistant to becoming demagnetized. This property makes steel a better choice for permanent magnets. 4. **Why Option D is Correct**: - Since steel retains magnetism better than iron, it is more suitable for applications requiring permanent magnets. This is why option D is the correct answer. ### Analysis of Other Options: - **Option A: is easily demagnetized by shaking vigorously**: - This statement is incorrect because steel is actually less likely to be demagnetized easily compared to iron. Shaking may demagnetize both materials, but steel's higher coercivity means it retains its magnetism better under such conditions. - **Option B: is an alloy of many metals**: - While steel is indeed an alloy, this statement does not directly relate to its suitability as a permanent magnet. The key factor is not the fact that it is an alloy, but rather how the alloy's composition affects its magnetic properties. - **Option C: is easily magnetized by alternating current through one cycle**: - This option is misleading. While steel can be magnetized, the ease of magnetization is not the primary reason it is preferred for permanent magnets. The focus should be on how well it retains magnetism after being magnetized, not just the ease of magnetization. ### Summary of Key Points: - Steel retains magnetism better than iron due to its higher coercivity. - Permanent magnets need to maintain their magnetic properties over time, making steel a more suitable choice. - Iron, while easily magnetized, tends to lose its magnetism more quickly than steel. - The composition of steel (as an alloy) contributes to its enhanced magnetic properties, but the key factor is its ability to retain magnetism. By understanding these concepts, you can better appreciate why steel is preferred for permanent magnets over iron.