Which of these substances has the highest boiling point?

The boiling point of a substance is influenced by factors such as molecular weight, intermolecular forces, and structure. Water is known for having exceptionally strong hydrogen bonding due to its polar covalent bonds and bent molecular shape. This strong attraction between water molecules requires more energy to break, resulting in a higher boiling point compared to many other substances.

Ethanol, while also capable of hydrogen bonding, has a lower boiling point than water. Ether, which primarily has weaker van der Waals forces and lacks strong hydrogen bonding, has a significantly lower boiling point than both water and ethanol. Glycerol, on the other hand, possesses high hydrogen bonding capability, which accounts for its relatively higher boiling point compared to ether and ethanol; however, it is still lower than that of water.

In conclusion, the combination of water's molecular structure and strong hydrogen bonds leads to a higher boiling point than that of ether, ethanol, and glycerol. Therefore, water stands as the substance with the highest boiling point among the choices presented.