The correct option for the question regarding which factor most significantly affects the electrical conductivity of gases at various pressures is **A. Temperature**. ### Detailed Explanation 1. **Understanding Electrical Conductivity in Gases**: - Electrical conductivity in gases refers to the ability of a gas to conduct electric current. This property is influenced by the presence of charged particles (ions and electrons) in the gas. - In gases, conductivity is generally low because the molecules are far apart, and there are fewer charged particles available to carry the current. 2. **Role of Temperature**: - **Temperature** affects the kinetic energy of gas molecules. As temperature increases, the kinetic energy of the gas molecules also increases, leading to more frequent and energetic collisions. - Higher temperatures can lead to increased ionization of gas molecules. When gas molecules gain enough energy (from thermal energy), they can lose electrons, creating free electrons and positive ions. This process is known as ionization. - The increased number of free charge carriers (ions and electrons) enhances the gas's ability to conduct electricity. Therefore, as temperature rises, the electrical conductivity of gases typically increases. 3. **Why Other Options Are Weaker**: - **B. Humidity**: While humidity can affect the conductivity of gases, especially in the context of air (where water vapor can ionize and contribute to conductivity), it is not as significant a factor as temperature. Humidity primarily affects the conductivity of air rather than pure gases. - **C. Ionization Energy**: Ionization energy is the energy required to remove an electron from an atom or molecule. While it is a fundamental property of the gas, it does not directly affect conductivity in the same way that temperature does. Higher ionization energy means that more energy is needed to ionize the gas, but it does not account for the number of charge carriers present at a given temperature. - **D. Molecular Mass**: The molecular mass of a gas can influence its density and the mean free path of molecules, but it does not have a direct and significant impact on electrical conductivity. Lighter gases may have higher mobility, but this does not necessarily correlate with higher conductivity unless temperature and ionization are also considered. ### Example Calculation To illustrate the effect of temperature on conductivity, consider the following: - The conductivity (\( \sigma \)) of a gas can be expressed in terms of the number density of charge carriers (\( n \)), their charge (\( q \)), and their mobility (\( \mu \)): \[ \sigma = n \cdot q \cdot \mu \] - As temperature increases, \( n \) (the number of charge carriers) increases due to increased ionization, and \( \mu \) (mobility) may also increase due to higher kinetic energy. Thus, \( \sigma \) increases. ### Common Pitfalls - Students may confuse the effects of humidity and temperature, thinking that humidity is the primary factor affecting conductivity in all gases. It is essential to recognize that while humidity can play a role, temperature has a more profound and direct impact on the ionization and mobility of charge carriers. - Misunderstanding the role of ionization energy can lead to the incorrect assumption that it is a primary factor in conductivity, rather than recognizing it as a property that influences how easily a gas can be ionized. ### Revision Summary - **Temperature** significantly affects the electrical conductivity of gases by increasing kinetic energy and ionization. - **Humidity** can influence conductivity but is less significant than temperature. - **Ionization energy** is a property of the gas, not a direct factor in conductivity. - **Molecular mass** affects density and mobility but does not directly correlate with conductivity. By focusing on temperature as the primary factor, students can better understand the behavior of gases in electrical applications and the principles of gas ionization.