**Correct Option: A. Iron** ### Detailed Explanation **Understanding Paramagnetism:** Paramagnetism is a form of magnetism that occurs in materials with unpaired electrons. Unpaired electrons have a magnetic moment due to their spin, which can align with an external magnetic field, causing the material to be attracted to the field. In contrast, materials with all paired electrons (like diamagnetic substances) do not exhibit this behavior. **Analyzing the Options:** 1. **Iron (Fe):** - Iron is a transition metal with an atomic number of 26. Its electron configuration is [Ar] 3d^6 4s^2. - In the 3d subshell, there are 6 electrons, and according to Hund's rule, they will occupy the available orbitals singly before pairing up. This results in 4 unpaired electrons in the 3d subshell. - Because of these unpaired electrons, iron exhibits paramagnetic properties. When placed in a magnetic field, these unpaired electrons align with the field, causing iron to be attracted to the magnet. 2. **Copper (Cu):** - Copper has an atomic number of 29, with an electron configuration of [Ar] 3d^10 4s^1. - In this configuration, all the 3d electrons are paired (10 electrons), and there is only one unpaired electron in the 4s subshell. However, the presence of a fully filled 3d subshell generally leads to a more stable, diamagnetic behavior. Thus, copper is not considered paramagnetic. 3. **Aluminum (Al):** - Aluminum has an atomic number of 13, with an electron configuration of [Ne] 3s^2 3p^1. - In this case, aluminum has one unpaired electron in the 3p subshell. However, aluminum is primarily classified as a paramagnetic material only under certain conditions and is generally considered weakly paramagnetic compared to iron. 4. **Gold (Au):** - Gold has an atomic number of 79, with an electron configuration of [Xe] 4f^14 5d^10 6s^1. - Similar to copper, gold has a filled 5d subshell and only one unpaired electron in the 6s subshell. This configuration leads to a more stable diamagnetic behavior, making gold not paramagnetic. ### Summary of Why Other Options Are Incorrect: - **Copper (B)**: Has a filled 3d subshell, leading to diamagnetism despite having one unpaired electron. - **Aluminum (C)**: While it has an unpaired electron, it is weakly paramagnetic and not as strongly paramagnetic as iron. - **Gold (D)**: Similar to copper, it has a filled 5d subshell and is primarily diamagnetic. ### Common Pitfalls: - Confusing the presence of unpaired electrons with the strength of paramagnetism. Just having unpaired electrons does not guarantee strong paramagnetic behavior. - Overlooking the influence of fully filled subshells, which can lead to diamagnetic properties even in the presence of unpaired electrons. ### Revision Summary: - **Paramagnetism** arises from unpaired electrons that align with magnetic fields. - **Iron** has multiple unpaired electrons, making it a strong paramagnetic material. - **Copper, Aluminum, and Gold** have configurations that lead to weaker or diamagnetic properties. - Always consider the electron configuration and the stability of filled subshells when determining magnetic properties.