**Correct Option: B. Lead** ### Detailed Explanation When it comes to shielding against high-frequency electromagnetic radiation, such as X-rays and gamma rays, the effectiveness of a material is determined by its density and atomic number. High-frequency electromagnetic radiation has high energy and can penetrate materials easily. Therefore, materials that are dense and have a high atomic number are more effective at absorbing or scattering this type of radiation. 1. **Understanding X-rays and Gamma Rays**: - X-rays and gamma rays are forms of ionizing radiation. They have very short wavelengths and high energy, which allows them to penetrate most materials. - To effectively shield against these rays, a material must be able to absorb or scatter the energy of the radiation. 2. **Properties of Lead**: - Lead (Pb) has a high atomic number (82) and is very dense (approximately 11.34 g/cm³). - The high density means that there are more atoms in a given volume to interact with the incoming radiation, which increases the likelihood of absorption or scattering. - Lead is commonly used in medical and industrial applications for radiation shielding, such as in X-ray rooms and nuclear facilities. 3. **Comparison with Other Options**: - **A. Wood**: - Wood is much less dense than lead and has a lower atomic number (carbon, hydrogen, and oxygen). While it can provide some shielding, it is not effective against high-energy radiation like X-rays and gamma rays. It would require a very thick layer of wood to provide any significant protection, which is impractical. - **C. Plastic**: - Plastic materials, such as polyethylene, are also low in density and atomic number. They can provide some shielding against lower-energy radiation but are ineffective against high-energy radiation like X-rays and gamma rays. They are often used in applications where low-energy radiation is present but not for high-energy radiation. - **D. Glass**: - Glass has a moderate density and atomic number compared to lead, but it is still not effective against high-energy radiation. Like wood and plastic, it would require a significant thickness to provide any meaningful protection, making it impractical for shielding against X-rays and gamma rays. ### Summary of Why Lead is the Best Option: - **High Density**: More mass per unit volume allows for better absorption of radiation. - **High Atomic Number**: Increases the likelihood of interactions with high-energy photons. - **Practical Use**: Widely used in medical and industrial settings for effective radiation shielding. ### Common Pitfalls: - Students may confuse the effectiveness of materials based on their everyday experiences (e.g., thinking wood or plastic can block radiation because they block visible light). - It’s important to remember that the effectiveness of shielding is not just about thickness but also about the material's density and atomic structure. ### Revision Summary: - Lead is the most effective material for shielding against high-frequency electromagnetic radiation due to its high density and atomic number. - Wood, plastic, and glass are less effective because they have lower densities and atomic numbers, requiring impractically thick layers for adequate protection. - Understanding the properties of materials is crucial for selecting appropriate shielding in practical applications involving radiation.