Assertion: Change of state is an example of isothermal process

Reason: Change of state from solid to liquid occurs only at melting point of solid and change of state from liquid to gas occurs only at boiling point of liquid. Thus, there is no change of temperature during change of state.

A change of state, such as solid to liquid (melting) and liquid to gas (vaporization), occurs at a constant temperature corresponding to the melting or boiling point of the substance. This temperature remains constant during the phase transition, and any heat added or removed during the process is used solely to facilitate the change of state rather than to change the temperature.

During these phase transitions:
- At the melting point, the solid absorbs heat energy, increasing the internal energy of its particles, until the solid changes to a liquid state. This energy goes into breaking the intermolecular bonds that hold the solid together.
- At the boiling point, the liquid absorbs heat energy, increasing the internal energy of its particles, until the liquid changes to a gaseous state. This energy is used to overcome the intermolecular forces and transform the liquid into vapor.

The temperature remains constant throughout these transitions because the added energy is used to break the bonds or forces between the particles rather than to raise the temperature. Once the phase transition is complete, further energy input will lead to a temperature increase in the new phase.