### Correct Option: C. Argon (Ar) #### Detailed Explanation: To understand why Argon (Ar) is the correct answer, we need to consider the properties of the gases listed and how they behave when ionized. 1. **Ionization and Electrical Conductivity**: - When a gas is ionized, it means that some of its atoms or molecules have lost or gained electrons, resulting in the formation of charged particles (ions). These charged particles can move freely and carry an electric current, which is what we refer to as electrical conductivity. - The ability of a gas to conduct electricity when ionized depends on several factors, including the number of available charge carriers (ions and electrons) and the ease with which the gas can be ionized. 2. **Properties of the Gases**: - **Oxygen (O₂)**: While oxygen can be ionized, it is a diatomic molecule that tends to form stable bonds. The ionization process can lead to the formation of reactive species, but it does not produce a high density of free electrons or ions compared to noble gases. - **Nitrogen (N₂)**: Similar to oxygen, nitrogen is also a diatomic molecule. It requires a significant amount of energy to ionize, and while it can conduct electricity when ionized, it does not do so as effectively as noble gases. - **Argon (Ar)**: Argon is a noble gas, which means it has a complete outer electron shell. This makes it relatively inert and stable under normal conditions. However, when ionized, argon can easily produce a large number of free electrons and ions, leading to high electrical conductivity. Noble gases are known for their ability to conduct electricity when ionized, as they do not readily form stable molecular bonds that would inhibit the movement of charge carriers. - **Hydrogen (H₂)**: Hydrogen is a diatomic molecule and can be ionized to produce protons and electrons. However, it does not have the same level of conductivity as argon when ionized, primarily because it does not produce as many free charge carriers in the ionized state. 3. **Comparison of Options**: - **A. Oxygen (O₂)**: While it can conduct electricity when ionized, it is less effective than argon due to its molecular structure and the stability of its bonds. - **B. Nitrogen (N₂)**: Similar to oxygen, nitrogen is less effective in conducting electricity when ionized compared to argon. - **C. Argon (Ar)**: This is the best option because it is a noble gas that, when ionized, produces a high density of free electrons and ions, leading to high electrical conductivity. - **D. Hydrogen (H₂)**: Although it can conduct electricity when ionized, it does not do so as effectively as argon due to fewer available charge carriers. #### Summary of Key Points: - **Ionization**: The process of losing or gaining electrons to form ions, which can conduct electricity. - **Noble Gases**: Argon, being a noble gas, has a complete electron shell and can produce many free charge carriers when ionized. - **Conductivity**: Argon exhibits the highest electrical conductivity among the options when ionized due to its ability to generate a large number of ions and electrons. ### Revision Summary: - Argon (Ar) is the most conductive gas when ionized due to its noble gas properties. - Ionization creates free electrons and ions, which are essential for electrical conductivity. - Oxygen (O₂), Nitrogen (N₂), and Hydrogen (H₂) are less effective in conducting electricity when ionized compared to Argon. - Noble gases like Argon are preferred for applications requiring high electrical conductivity in their ionized state.