### Correct Option: A. Reduced pressure and high current #### Explanation of the Correct Answer: 1. **Understanding Gas Conductivity**: - Gases are generally poor conductors of electricity because their molecules are far apart, which makes it difficult for electric charges to move through them. However, under certain conditions, gases can become conductive. 2. **Reduced Pressure**: - When the pressure of a gas is reduced, the density of the gas decreases. This means that the gas molecules are further apart, which can lead to a situation where the gas can be ionized more easily. Ionization is the process where gas molecules lose or gain electrons, creating charged particles (ions) that can carry electric current. 3. **High Current**: - When a high current is applied to a gas, it can provide enough energy to ionize the gas molecules. This ionization creates free electrons and positive ions, which can move and carry the electric current. Therefore, a combination of reduced pressure (which facilitates ionization) and high current (which provides the energy needed for ionization) allows the gas to conduct electricity effectively. 4. **Practical Example**: - A common example of this phenomenon is in gas discharge tubes, such as neon lights. When the pressure inside the tube is low and a high voltage is applied, the gas becomes ionized, allowing it to conduct electricity and emit light. #### Why the Other Options are Incorrect: - **Option B: Increased Magnetic Field**: - An increased magnetic field does not directly affect the conductivity of a gas. While magnetic fields can influence the motion of charged particles (like electrons), they do not facilitate the ionization of gas molecules or enhance the gas's ability to conduct electricity. Therefore, this option is not relevant to the conductivity of gases. - **Option C: Reduced Pressure and Reduced Potential**: - While reduced pressure can help in ionization, reduced potential (voltage) would not provide the necessary energy to ionize the gas. A lower potential means less energy is available to create free charges, which is essential for conduction. Thus, this option is contradictory and does not support the conductivity of the gas. - **Option D: Exposure to Visible Light**: - Exposure to visible light can cause some gases to ionize, but this effect is generally weak compared to the effects of high current. Most gases require significant energy input (like that from a high voltage) to become conductive. Therefore, while light can play a role in some specific cases (like photoionization), it is not a reliable method for making a gas conductive compared to the combination of reduced pressure and high current. ### Summary of Key Points: - Gases can conduct electricity when they are ionized, which occurs more readily at reduced pressure. - High current provides the energy needed to ionize gas molecules, creating free electrons and ions. - Increased magnetic fields and reduced potential do not enhance gas conductivity. - Visible light can cause ionization but is less effective than high current in practical applications. This understanding is crucial for grasping the behavior of gases in electrical applications and can help in solving related problems in physics.