Water can exist in how many physical states?

• A. One
• B. Two
• C. Three
• D. Four

Answer: (C)

Water can exist in three common physical states. In a solid, it forms ice with a definite shape and volume. In a liquid, it remains a definite volume but takes the shape of its container. In a gas, water vapor expands to fill the space and has no fixed shape or volume. These states change through energy added or removed: freezing and melting between solid and liquid, vaporization and condensation between liquid and gas, and sublimation between solid and gas. A rare, explicitly different state called a supercritical fluid can occur at very high temperature and pressure, but in standard classroom contexts we count three states.