Question

While boiling water temperature remains constant at 100c till whole of water vapourises .explain

Answer 1

Vapourisation is just the change of state of liquid, not the temperature.

Take a solid ice cube of temperature 0 degree celsius. When we heat it the heat energy will be first used to convert the state solid to liquid, ie. it will be converted into liquid having temperature 0 degree celsius. After changing the state the energy is used to increase the temperature. When the temperature is 100 degree celsius, the water starts boiling. On continuous heating the energy will be used to change the state of water from liquid to steam having temperature 100 degree celsius itself.