**Correct Option: B. is a poor conductor** ### Detailed Explanation: To understand why water is considered a poor thermometric liquid, we need to analyze the properties of water in the context of thermometry and how it compares to other liquids typically used in thermometers. 1. **Thermometric Liquids**: A thermometric liquid is a liquid used in thermometers to measure temperature. The ideal thermometric liquid should have certain properties, including: - High thermal expansion - Low thermal conductivity - Non-wetting properties with the glass of the thermometer - A low freezing point and a high boiling point - Low vapor pressure 2. **Water's Properties**: - **Thermal Conductivity**: Water has relatively low thermal conductivity compared to metals and some other liquids. This means it does not transfer heat as efficiently. In a thermometer, if the liquid does not conduct heat well, it may not respond quickly to temperature changes, leading to inaccurate readings. - **Thermal Expansion**: Water does expand when heated, but its expansion is not as predictable as that of other liquids like mercury, which is commonly used in thermometers. - **Wetting Properties**: Water tends to wet glass, which can cause issues in reading the thermometer accurately. When a liquid wets the glass, it can cling to the sides, leading to a meniscus that is difficult to read. - **Vapor Pressure**: Water has a relatively high vapor pressure at higher temperatures, which can lead to evaporation and inaccuracies in temperature readings. 3. **Why Option B is Correct**: - The primary reason water is a poor thermometric liquid is its low thermal conductivity. This property means that water does not quickly equalize its temperature with the environment, making it less effective for precise temperature measurements. In contrast, liquids like mercury have high thermal conductivity, allowing them to respond rapidly to temperature changes. ### Analysis of Other Options: - **Option A: is opaque**: - This option is incorrect because the opacity of a liquid does not significantly affect its ability to measure temperature. While transparency can be beneficial for visual readings, it is not a critical property for thermometric liquids. Many thermometric liquids are opaque, yet they can still function effectively. - **Option C: wets glass**: - While it is true that water wets glass, this property is not the primary reason it is a poor thermometric liquid. Wetting can lead to difficulties in reading the thermometer, but it does not directly affect the liquid's ability to conduct heat or respond to temperature changes. - **Option D: has low vapor pressure**: - This option is incorrect because water actually has a relatively high vapor pressure, especially at elevated temperatures. A low vapor pressure is generally desirable in a thermometric liquid to prevent evaporation, which can lead to inaccuracies. Therefore, this statement does not support the claim that water is a poor thermometric liquid. ### Summary of Key Points: - Water is a poor thermometric liquid primarily due to its low thermal conductivity, which affects its responsiveness to temperature changes. - Other properties, such as wetting glass and vapor pressure, also play a role but are not the main reasons for its ineffectiveness as a thermometric liquid. - Mercury is often preferred in thermometers due to its high thermal conductivity, predictable expansion, and low vapor pressure. ### Revision Summary: - Water's low thermal conductivity makes it slow to respond to temperature changes. - It tends to wet glass, complicating accurate readings. - High vapor pressure at elevated temperatures can lead to evaporation issues. - Mercury is often preferred for thermometers due to its superior properties.