Latent Heat as Energy for Phase Change

Steps:

• Recall that latent heat is thermal energy absorbed or released during a phase change without temperature variation.
• For gap 1, identify the quantity needed to break molecular bonds: energy, as heat transfer overcomes intermolecular forces.
• For gap 2, note the result of this energy input: a change in physical state (e.g., solid to liquid).
• Match options: "energy state" fits both gaps logically.

Why A is correct:

• By definition, latent heat is the energy per unit mass required to change a substance's state, such as during melting or boiling, without altering temperature (Q = mL, where L is specific latent heat).

Why the others are wrong:

• B: "Force" misrepresents heat as mechanical force, not thermal energy.
• C: "Force" and "temperature" confuse energy input with unrelated concepts; temperature stays constant during phase changes.
• D: "Temperature" first ignores that latent heat is energy, not temperature change.

Final answer: A