Question

give reason for

vapourization takes place at all temperature but boiling takes place at boiling point

Answer 1

As we know evaporation is the surface phenomenon. The molecules of liquid only evaporate from surface at any temperature.
The reason for evaporation at any temperature is the molecules of the substance are always in motion. When molecules near the surface of the liquid get enough kinetic energy from internal motion collision or from surroundings , it can easily break the force of attraction from lower level of molecules and escape to atmosphere as gas.The motion of molecules zero near absolute zero temperature. So, the liquid molecules can escape the surface at all temperature.
While Boiling is bulk phenomenon. That is all the molecules in bulk get sufficient energy to change in gas phase. This happen only when vapour pressure of liquid becomes equal to atmospheric pressure. So, the temperature is also specific for boiling.