Under standard conditions, at what temperature does water freeze?

• A. 0°C
• B. 100°C
• C. -10°C
• D. 25°C

Answer: (A)

Freezing point is the temperature at which a liquid becomes a solid when pressure is kept constant. Under standard atmospheric pressure, water reaches this transition at a specific temperature, marking the boundary between the liquid and solid phases. The correct choice is the one that describes this liquid-to-solid change under one atmosphere, since it exactly identifies the point where water stops being liquid and becomes ice as you lower the temperature. The other temperatures listed correspond to other states: a much higher temperature would be where water boils into steam, while a lower temperature would place water in a solid state already, not at the boundary from liquid to solid.