Which of the following will cause liquid water to freeze and become ice?

• A. Lowering the temperature below 0 ^ext{o}C
• B. Adding sodium chloride (NaCl) to water at 0 ^ext{o}C
• C. Adding sugar to water at 0 ^ext{o}C
• D. Increasing the pressure above atmospheric pressure at 0 ^ext{o}C

Answer: (A)

Verified step by step guidance

1. Understand the phase change of water: water freezes and becomes ice when its temperature drops below its freezing point, which is 0 \^\{\text{o}\}C at standard atmospheric pressure.
2. Recognize that lowering the temperature below 0 \^\{\text{o}\}C removes thermal energy from the water, allowing the molecules to arrange into a solid crystalline structure (ice).
3. Consider the effect of adding sodium chloride (NaCl): salt lowers the freezing point of water (freezing point depression), so adding NaCl actually prevents freezing at 0 \^\{\text{o}\}C.
4. Consider the effect of adding sugar: like salt, sugar also lowers the freezing point of water, so it will not cause water to freeze at 0 \^\{\text{o}\}C.
5. Consider the effect of increasing pressure: for water, increasing pressure at 0 \^\{\text{o}\}C tends to favor the liquid phase rather than ice, so it does not cause freezing under these conditions.