Final answer:
Water (H2O) has the highest boiling point among H2O, HBr, H2Se, and PH3 due to its ability to form strong hydrogen bonds, requiring more energy to reach the boiling point.
Step-by-step explanation:
The compound with the highest boiling point among H2O, HBr, H2Se, and PH3 is H2O (water). This is because water is capable of forming hydrogen bonds, which are much stronger intermolecular forces compared to the predominantly London dispersion forces present in HBr, H2Se, and PH3. Due to these strong hydrogen bonds, more energy is required to break these interactions in the liquid phase, hence a higher boiling point. While HBr, a hydrogen halide, also experiences dipole-dipole interactions, they are not as strong as the hydrogen bonds in water. Similarly, PH3 and H2Se are heavier molecules that might have stronger London dispersion forces, yet these do not compete with the strength of hydrogen bonding in water.