What defines the transition of water from ice to liquid state?

• A. The addition of latent heat
• B. The removal of heat only
• C. The addition of sensible heat only
• D. The change in atmospheric pressure

Answer: (A)

The transition of water from ice to liquid is defined by the addition of latent heat, which is the heat energy required to change a substance's state without changing its temperature. In this case, when ice is supplied with heat, it absorbs that energy and uses it to break the bonds that hold the ice molecules in a solid state, leading to a phase change into liquid water.

During this process, the temperature of the ice remains constant at 0 degrees Celsius (at standard atmospheric pressure) until all the ice has melted completely into liquid water. This energy absorbed is termed latent heat because it is 'hidden' in the sense that it does not increase the temperature of the substance at this transition point.

The other options do not accurately describe the process: the removal of heat would not cause melting, while adding only sensible heat would raise the temperature without causing the change of state, and atmospheric pressure influences melting points but isn't a direct definition of the transition itself. Thus, the correct answer emphasizes the role of latent heat in facilitating the shift from ice to liquid water.