What is sub-cooled liquid water?

Sub-cooled liquid water refers to water that is in a liquid state but has a temperature that is lower than its freezing point while still remaining in the liquid phase. In this state, the water is not frozen despite being below the temperature typically associated with freezing, which is 0 degrees Celsius (32 degrees Fahrenheit) at standard pressure. This phenomenon can occur under certain conditions, such as when water is subjected to pressure, preventing it from transitioning to ice.

The other options do not accurately describe sub-cooled liquid water: boiling water is in a gas phase; water at the freezing temperature may contain ice, indicating it is not purely in a sub-cooled state; and water above the boiling point is in a vapor state. Thus, option B accurately captures the unique characteristics of sub-cooled liquid water.