What is the standard method for calibrating a thermometer?

The correct approach to calibrating a thermometer is to use the defined freezing and boiling points of water, which are universally acknowledged reference points. Specifically, ice water has a freezing point of 32 degrees Fahrenheit (0 degrees Celsius), while boiling water reaches 212 degrees Fahrenheit (100 degrees Celsius) at standard atmospheric pressure.

Using either 32 degrees in ice water or 212 degrees in boiling water provides an accurate calibration method because these temperatures are consistently reliable under normal conditions. This approach helps ensure that the thermometer gives accurate readings across various uses and environments.

In contrast, referencing either of the other choices would not provide the same level of calibration accuracy. For example, calibrating at 100 degrees in ice water does not align with standard temperature references, and using 50 degrees in room temperature water lacks the precision offered by the boiling and freezing points. These points ensure that the thermometer can perform accurately within a wide temperature range, making the method referenced in the correct answer essential for reliable temperature measurement.