Final answer:
The gas state is where entropy is highest among the options provided, due to the molecules being more spread out and moving faster compared to those in liquids and solids. Phases where molecules can change their positions include liquids, gases, and plasmas.
Step-by-step explanation:
The highest entropy state for any given substance is typically the plasma state, where particles are ionized and roam freely at high energy levels. However, those options are not given in the question, so within the standard three states of matter, the gas state is the one where entropy is highest. This is because, in a gaseous state, the molecules of the substance are much more spread out and move at higher speeds, compared to a liquid or a solid, resulting in a greater number of possible microstates and thus higher entropy.
Regarding the phases of matter where molecules are capable of changing their positions, the correct option is c. liquid, gas, plasma. Molecules in these phases are not fixed in position as in a solid; they can move freely or flow past one another, increasing their disorder and entropy. In the case of a plasma, which has the highest entropy of all, the particles are in an even more disordered state than in a gas due to ionization and high energy interactions.