Final answer:
The volume of a substance increases the most during vaporization, the transition from liquid to gas, due to the large separation between gas particles.
Step-by-step explanation:
The change of state during which the volume of a substance increases the most is vaporization (c). This involves the transition of a substance from a liquid to a gas, which occupies much more volume due to the significant increase in the energetic state of the particles and the larger separation between them. Among the options, sublimation (d) also represents a substantial increase in volume, as it involves the transition from a solid directly to a gas, but vaporization generally involves a greater volume expansion. It is important to note that the increase in volume is much less for the other phase changes mentioned like melting (b), where a solid becomes a liquid, or deposition (a), where a gas becomes a solid.