A thermometer suitable for measuring 2000 °C is

To measure extremely high temperatures, such as 2000 °C, a total radiation pyrometer is the appropriate instrument. Total radiation pyrometers function by detecting the thermal radiation emitted by an object and converting this radiation into a temperature reading. This method is particularly effective for high-temperature measurements where direct contact methods, such as mercury or gas thermometers, are impractical or unsafe.

Mercury thermometers and gas thermometers are typically limited to much lower temperature ranges and would not withstand the extreme heat of 2000 °C. Vapor pressure thermometers also cannot measure such high temperatures, as they rely on the vapor pressure of a liquid, which would not be stable at these levels. Total radiation pyrometers, however, are designed specifically for such conditions, making them ideal for industrial applications involving furnaces, kilns, and other high-temperature environments. Therefore, the correct answer is [C] Total radiation pyrometer.