When the intermolecular forces of attraction in a liquid become stronger, the boiling point of the liquid increases. This is because stronger intermolecular forces require more energy to overcome them. During the boiling process, molecules in the liquid need enough energy to break free from these attractive forces so they can escape into the gas phase.
For instance, consider water and alcohol. Water has stronger hydrogen bonds compared to the weaker van der Waals forces in alcohol. As a result, water has a higher boiling point (100°C) than alcohol, which boils at a lower temperature (about 78°C). This illustrates how the strength of intermolecular forces directly influences the boiling point of substances.