Why are the intermolecular attractions in H2O (g) much weaker than H2O (i) or H2O (s)

The average distances between gaseous molecules are greatest of all phases

Explanation:

According to Coulomb's Law, the force between charges is inversely proportional to the square of a distance between two charges.

We know that solids are generally the most dense states (although ice is less dense than liquid water) in which the average distances between molecules are minimal. This is followed by liquids in which distances are greater than those in solids.

The distances between molecules in gaseous substances, on the other hand, are greatest, so that the attraction forces in gases are lowest according to Coulomb's Law.