Identify four unusual properties of water that are a direct result of hydrogen bonding, and explain each in terms of hydrogen bonding.

All this below

High boiling and melting points: Hydrogen bonds increase the amount of energy required for phase changes to occur, thereby raising the boiling and melting points.

High specific heat: Hydrogen bonds increase the amount of energy required for molecules to increase in speed, thereby raising the specific heat.

Lower density as a solid than as a liquid: Hydrogen bonds increase the volume of the solid by holding molecules apart, thereby decreasing the density.

High surface tension: Hydrogen bonds produce strong intermolecular  attractions, which increase surface tension.

the answer is option a.