ANS:B - Bimetallic

The type of thermometer that cannot measure sub-zero (< 0°C) temperatures is the vapor pressure thermometer.

Explanation:

1. Mercury in Glass Thermometer:
   • A mercury-in-glass thermometer can measure temperatures well below freezing (below 0°C) by using the expansion and contraction of mercury with temperature changes.
2. Bimetallic Thermometer:
   • Bimetallic thermometers typically operate over a wide range of temperatures, including sub-zero temperatures. They use the differential expansion of two metals to indicate temperature.
3. Resistance Thermometer (RTD):
   • Resistance thermometers, such as those made with platinum (PT100 sensors), can measure temperatures from well below freezing to high temperatures. They rely on the change in electrical resistance with temperature.
4. Vapor Pressure Thermometer:
   • Vapor pressure thermometers use the vapor pressure of a volatile fluid, such as alcohol or ether, which changes with temperature. These thermometers typically do not perform accurately below 0°C due to the properties of the fluid and vapor pressure curves.

Conclusion:

While all thermometers have specific temperature ranges for accurate measurement, the vapor pressure thermometer is particularly limited in its ability to measure sub-zero temperatures effectively. This limitation arises from the nature of the fluid and the mechanics of vapor pressure measurement, which are less reliable at very low temperatures.