The melting point of a solid depends on the strength of the intermolecular forces holding the molecules together. In the case of water, which is a polar molecule, it experiences stronger intermolecular forces such as hydrogen bonding between its molecules. These forces require more energy to overcome, resulting in a higher melting point for water compared to a non-polar molecule like nitrogen which only experiences weaker van der Waals forces between its molecules. Therefore, the stronger intermolecular forces in polar substances lead to a higher melting point compared to non-polar substances.
