Question

It is said that when we boil something it changes its state from solid state to liquid state but when we boil an egg it changes its state from liquid to solid. Why does this happen?

Answer 1

The liquid turns to a gas on heating only when a boiling point of liquid is reached.
And egg is made up of proteins ,so when an egg is boiled at high temperature,entropy of it's molecule increases .This increase in entropy causes denaturation of protein present in eggs and results in coagulation of proteins. Thus it gets solidified.
Details of the entropy concept and its effect on egg will be taught to you in your higher classes.