Which of the following bonds or interactions must be overcome for water (H_2O) to change from a liquid to a gas?

• A. Hydrogen bonds between water molecules
• B. Metallic bonds within water molecules
• C. Ionic bonds between H^+ and OH^- ions
• D. Covalent O–H bonds within a water molecule

Answer: (A)

Verified step by step guidance

1. Understand the physical change involved: changing water from liquid to gas is a phase change called vaporization, which involves overcoming intermolecular forces, not breaking bonds within molecules.
2. Identify the types of bonds and interactions listed: hydrogen bonds between water molecules, metallic bonds within water molecules, ionic bonds between H^+ and OH^- ions, and covalent O–H bonds within a water molecule.
3. Recall that water molecules are held together in the liquid phase primarily by hydrogen bonds, which are intermolecular forces between the partially positive hydrogen of one molecule and the partially negative oxygen of another.
4. Recognize that metallic bonds do not exist within water molecules, as water is a molecular compound, not a metal.
5. Note that covalent O–H bonds are intramolecular bonds holding atoms together within a single water molecule and are not broken during vaporization; similarly, ionic bonds between H^+ and OH^- ions are not relevant here because pure water is mostly molecular, not ionic.