A glass tumbler containing hot water is kept in the freezer compartment of a refrigerator (temperature < 0°C). If you could measure the temperature of the content of the tumbler, which of the following graphs (Fig.1.2) would correctly represent the change in its temperature as a function of time.

The correct answer is (a). The temperature of the water in a tumbler will fall initially till it reaches 0 °C, the freezing point of water. After reaching the freezing point, the temperature will remain constant till all the water has been converted into ice. And, after this temperature would further decrease below 0 °C.