Final answer:
Calibrating a thermometer with a melting point apparatus involves submerging it in ice water to ensure it reads 0 °C, the reference freezing point of water on the Celsius scale.
Step-by-step explanation:
When calibrating a thermometer with a melting point (m.p.) apparatus, the correct option is b) Submerged in ice water. This is because one of the reference points commonly used for calibration is the freezing point of water, which is 0 °C on the Celsius scale. The procedure involves ensuring that the thermometer reads the correct temperature when submerged in ice water, which, under normal atmospheric pressure, provides a stable and reproducible temperature reference.
In addition to calibration with ice water, it is also common to use the boiling point of water as another reference point for calibration. However, the question specifically mentions using a melting point apparatus, which indicates the focus is on the calibration of the thermometer at the freezing point of water.