What leads to the high melting and boiling points of water?

The high melting and boiling points of water can be attributed to the presence of strong hydrogen bonds between water molecules. Water is a polar molecule, where the oxygen atom has a partial negative charge and the hydrogen atoms have partial positive charges. This polarity gives rise to hydrogen bonding, which occurs when the positively charged hydrogen atom of one water molecule is attracted to the negatively charged oxygen atom of another water molecule.

These hydrogen bonds are relatively strong compared to other types of intermolecular interactions, such as dispersion forces or weak dipole-dipole interactions. As a result, a significant amount of energy is required to break these hydrogen bonds, which leads to higher melting and boiling points.

In contrast, while other options touch upon certain aspects of molecular interactions, they do not adequately explain the specific reason for water's high melting and boiling points as effectively as the strong hydrogen bonds do. For instance, weak dipole-dipole interactions do not significantly contribute to the thermal properties of water, and while the electronegativity difference does affect polarity, it is the hydrogen bonding that directly impacts the energy required for phase changes. Additionally, the atomic mass of the constituent atoms plays a less important role in influencing melting and boiling points compared to the strength of intermolecular forces.