Explanation:
When heat is supplied to the liquid through the burner then portion of liquid at the bottom will start to heat first.
This means molecules at the bottom will start to gain kinetic energy and thus intermolecular forces between them start to decrease.
As a result, they will start to move from their initial position. That is, molecules per unit volume will decrease. Hence, density will decrease and the liquid will rise upward.
Whereas when all the molecules of liquid are heated up then it will release energy into the atmosphere.
Thus, we can conclude that this happens to the portion of liquid that first begins to warm.
