Final answer:
The equilibrium fraction of lattice sites that are vacant in silver at a specific temperature corresponds to its melting point, which is when the solid and liquid phases of the substance are in equilibrium.
Step-by-step explanation:
The equilibrium fraction of lattice sites that are vacant in silver at a given temperature is related to its melting point. The melting point is the temperature at which the solid and liquid phases of a substance are in equilibrium. At this temperature, the individual atoms in the lattice have enough kinetic energy to overcome the attractive forces holding them together in the solid state, creating vacancies as some atoms move into the liquid phase.
Regarding the options provided in the schoolwork question, boiling point refers to the temperature at which a substance changes from a liquid to a gas throughout the liquid, vapor pressure is the pressure of a vapor in thermodynamic equilibrium with its condensed phases in a closed system, molar mass is the mass of one mole of a substance, and the correct answer, melting point, is the temperature at which a substance changes from a solid to a liquid state.