### Correct Option: A. Temperature #### Detailed Explanation: Electrical conductivity in gases, especially at low pressures, is primarily influenced by temperature. Here’s a step-by-step breakdown of why temperature is the most significant factor: 1. **Understanding Electrical Conductivity**: - Electrical conductivity refers to a material's ability to conduct electric current. In gases, this occurs when gas molecules are ionized, allowing free electrons to move and carry charge. 2. **Effect of Temperature**: - As temperature increases, the kinetic energy of gas molecules also increases. This heightened energy leads to more frequent and energetic collisions between gas molecules. - At higher temperatures, more molecules can gain enough energy to overcome the ionization energy barrier, resulting in a greater number of free electrons and positive ions. This increase in charge carriers enhances the gas's ability to conduct electricity. 3. **Ionization Process**: - In gases, ionization can occur through various means, such as thermal ionization (where heat provides the energy needed to ionize atoms) or through collisions with high-energy photons. - At low pressures, the density of gas molecules is low, which means that the likelihood of collisions is reduced. However, increasing the temperature compensates for this by increasing the energy of the molecules, thus facilitating more ionization events. 4. **Comparison with Other Options**: - **B. Humidity**: While humidity can affect the conductivity of gases, especially in the context of air (where water vapor can introduce additional charge carriers), its effect is not as significant as temperature. In low-pressure conditions, the presence of water vapor may not be sufficient to enhance conductivity compared to the effects of temperature. - **C. Gas Density**: At low pressures, gas density is inherently low, which means that the number of molecules available for collisions is reduced. While density can influence conductivity, it is the temperature that primarily drives the energy of the molecules and the rate of ionization. - **D. Ionization Energy**: Ionization energy is a property of the gas itself and determines how easily a gas can be ionized. However, it does not change with conditions like temperature or pressure. Therefore, while it is a factor in determining the conductivity of a specific gas, it does not significantly affect the overall conductivity of gases at low pressures compared to temperature. #### Example Calculation: To illustrate the effect of temperature on conductivity, consider the following simplified scenario: - Assume a gas at room temperature (300 K) has a certain number of free electrons. If the temperature is increased to 600 K, the kinetic energy of the gas molecules increases, leading to a higher rate of ionization. - The number of free electrons can be approximated using the Boltzmann distribution, which shows that the number of particles with energy greater than the ionization energy increases exponentially with temperature. #### Common Pitfalls: - Students may confuse the effects of humidity and temperature, thinking that humidity is the primary factor affecting conductivity. It is essential to recognize that while humidity can introduce additional charge carriers, temperature has a more profound effect on the overall conductivity of gases. - Another common mistake is to overlook the significance of low pressure in the context of gas density. At low pressures, the density is low, but the temperature can still significantly influence the number of ionized particles. ### Revision Summary: - **Temperature significantly increases the kinetic energy of gas molecules, enhancing ionization and conductivity.** - **Humidity can affect conductivity but is less significant than temperature at low pressures.** - **Gas density at low pressures reduces the number of collisions, making temperature the key factor for conductivity.** - **Ionization energy is a property of the gas and does not change with external conditions, thus having a lesser impact on conductivity compared to temperature.**