The correct option for the question regarding which factor primarily affects the electrical conductivity of gases at low pressures is **C. Ionization of gas molecules**. ### 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 gases have fewer charge carriers (like free electrons or ions) available to carry the current. 2. **Role of Ionization**: - At low pressures, the density of gas molecules is low, which means that the likelihood of collisions between gas molecules is reduced. When an electric field is applied, the gas molecules can become ionized, meaning that they lose or gain electrons and form charged particles (ions). - Ionization is crucial because it creates free charge carriers (electrons and positive ions) that can move under the influence of an electric field, thus increasing the gas's conductivity. The more ionization that occurs, the higher the conductivity. 3. **Why Other Options Are Weaker**: - **A. Temperature of the gas**: While temperature does affect conductivity (higher temperatures can increase the energy of gas molecules and lead to more ionization), it is not the primary factor at low pressures. The effect of temperature is more pronounced in denser gases where collisions are more frequent. - **B. Presence of impurities**: Impurities can affect conductivity, but their impact is generally secondary to the ionization process. In a pure gas, ionization will have a more significant effect on conductivity than the presence of impurities. - **D. Type of gas molecules**: Different gases have different ionization energies and properties, which can affect conductivity. However, the primary mechanism that enhances conductivity at low pressures is still the ionization of the gas molecules rather than the type of gas itself. ### Summary of Key Points - **Ionization is the primary factor** affecting electrical conductivity in gases at low pressures because it creates free charge carriers. - **Temperature and impurities** can influence conductivity but are secondary to the effects of ionization. - **Type of gas molecules** matters, but the ionization process is the key mechanism for conductivity enhancement. ### Revision Summary - Electrical conductivity in gases is primarily influenced by the **ionization of gas molecules**. - At low pressures, the **density of gas molecules is low**, leading to fewer collisions and less conductivity. - **Temperature** and **impurities** can affect conductivity but are not the main factors at low pressures. - Understanding the **ionization process** is crucial for grasping how gases conduct electricity.