Boiling occurs only on the surface of liquid.
Here think about the word ‘only’ here. Evaporation is a surface phenomenon. But what about boiling?
Let's recall the definition of boiling to answer this question.
Boiling is a special case of evaporation. It is the rapid conversion of a liquid into vapour by means of formation of bubbles.
During boiling, vaporization is not restricted to the surface only but takes place throughout the bulk of the liquid.