Question

Evaporation occurs at all the temperture whereas boiling occurs at fixwd teperature why

Answer 1

When water meets dry air, it is not in equilibrium. So, water vapors evaporates off the surface into the air to create equilibrium. Thus it happens at all temperature to achieve equilibrium. 
While at 100 degree, water starts boiling and began to break the bond and change into steam. 

Answer 2

Explanation:

When the air molecules strike the surface, they are going to impart some energy to the water molecules. If this energy is sufficient enough to change the phase of water molecules, we experience a phenomenon, EVAPORATION. So, i