The correct option for the question regarding which factor primarily affects the electrical conductivity of gases at low pressures is **C. Presence of ionizing radiation**. ### Detailed Explanation 1. **Understanding Electrical Conductivity in Gases**: - Electrical conductivity in gases refers to the ability of the gas to conduct electric current. In gases, this conductivity is generally very low compared to solids and liquids because gas molecules are far apart, making it difficult for charge carriers (like electrons or ions) to move freely. 2. **Low Pressure Conditions**: - At low pressures, the density of gas molecules decreases, which means there are fewer molecules available to collide and transfer charge. This condition can significantly influence how well the gas can conduct electricity. 3. **Role of Ionizing Radiation**: - Ionizing radiation (such as X-rays, gamma rays, or high-energy particles) can provide enough energy to gas molecules to strip electrons away, creating ions. This process is known as ionization. - When gas molecules are ionized, they produce free electrons and positive ions. These charged particles can move under the influence of an electric field, thus increasing the gas's electrical conductivity. - Therefore, the presence of ionizing radiation is a primary factor because it directly increases the number of charge carriers in the gas, enhancing its ability to conduct electricity. ### Why the Other Options Are Weaker - **A. Temperature of the gas**: - While temperature does affect the kinetic energy of gas molecules and can influence conductivity, its effect is less pronounced at low pressures compared to the presence of ionizing radiation. At low pressures, the number of collisions between molecules decreases, and thus the effect of temperature on conductivity is not as significant as the effect of ionization. - **B. Type of gas molecules**: - Different gases have different ionization energies and molecular structures, which can affect their conductivity. However, at low pressures, the type of gas is less critical than the presence of ionizing radiation. For example, noble gases like helium or neon are less likely to ionize than more reactive gases, but without ionizing radiation, their conductivity remains low regardless of their type. - **D. Humidity levels in the gas**: - Humidity refers to the presence of water vapor in the gas. While humidity can affect the conductivity of air (for example, moist air can conduct electricity better than dry air), this effect is generally more relevant in the context of higher pressures and does not primarily influence the conductivity of gases at low pressures. The presence of water vapor does not create free charge carriers in the same way that ionizing radiation does. ### Summary of Key Points - **Electrical conductivity in gases is primarily influenced by the presence of charge carriers.** - **Ionizing radiation creates free electrons and ions, significantly enhancing conductivity.** - **Temperature and type of gas have secondary effects, especially at low pressures.** - **Humidity affects conductivity but is less significant than ionization in low-pressure scenarios.** This understanding is crucial for grasping the behavior of gases under different conditions, especially in applications involving electrical discharges, gas ionization, and plasma physics.