What property of water allows it to serve as both a hydrogen bond donor and acceptor?

The property of water that allows it to serve as both a hydrogen bond donor and acceptor is its dipole moment. Water molecules are polar because of the difference in electronegativity between the oxygen and hydrogen atoms. The oxygen atom is more electronegative, which creates a partial negative charge on the oxygen and a partial positive charge on the hydrogens. This polarization allows water molecules to interact with each other through hydrogen bonding.

In this context, the oxygen atom can act as a hydrogen bond acceptor due to its partial negative charge, while each hydrogen atom can serve as a hydrogen bond donor because of their partial positive charges. This unique ability to both donate and accept hydrogen bonds is essential for many of water's physical properties and its role in biological systems.

The other options, while relevant to understanding various features of water, do not explain the capacity for hydrogen bonding. Surface tension arises from cohesive forces between water molecules, high specific heat is a consequence of hydrogen bonding that allows water to resist temperature changes, and density anomalies, such as ice being less dense than liquid water, are also related to hydrogen bond structure but do not define the molecules' ability to donate and accept hydrogen bonds. Thus, the dipole moment is the key property that enables