What is the freezing point of water under standard conditions?

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

Answer: (A)

The key idea is the temperature at which water changes from liquid to solid when the pressure is 1 atmosphere. At standard conditions, pure water freezes at 0°C (273.15 K). The value 100°C is the boiling point at 1 atm, not the freezing point. -10°C is well below freezing, so water would already be solid, and 25°C is room temperature, far above the freezing point. So 0°C is the correct freezing point under standard conditions.