Here it says select a substance with greatest molar entropy. So remember when comparing the entropies of different substances, the first thing we look at is their phase. So gases have the most entropy, then liquids, then solids. If we take a look at our options here, we have 3 gases. They would have the greatest entropy. So that means A is out, B is out, and D is out.
The next thing we look at to break the tie is their complexity. Basically, the more atoms comprising the substance, the greater its entropy. Ammonia has four atoms involved because it has one nitrogen and three hydrogens. Carbon dioxide only has three atoms since it's one carbon and two oxygens. And sulfur trioxide has four atoms because it's one sulfur and three oxygens. So E is out.
Now we see that ammonia and sulfur trioxide have the same complexity. So the last thing we look at to break the tie is their mass. The greater the mass of the substance, the greater the entropy here. If we compare the masses of ammonia versus sulfur trioxide, sulfur trioxide weighs more. Therefore it's going to have the higher molar entropy. So here the answer is option F.
