There is a huge amount of fresh water on Earth. Which of the following are reasons that much of it is unusable?

mostly the frozen stuff is in a remote location so both frozen and remote location apply about the same.  Basically, most of the water is not where the people are who would use it.  Doesn't matter if it is or isn't frozen; it is too much trouble to get it to where people would want it. Being frozen just makes it even harder, is all.

Frozen and in a remote location

ii it's frozen would be my guess.

All of them are reasons for very large amounts of freshwater being unusable, but "much of it"?  It's a poor question because "much" isn't clearly defined and is highly subjective.  Well, not to split hairs, but polluted water isn't unusable, just unusable for some things and non-potable.  As for "remote location," the hugest freshwater aquifer in the world is directly underneath the Sahara, but it's inaccessible because it is so far down.  As for "frozen," 70% of Earth's freshwater is frozen, so that's most of it, but "most of it" is a higher standard than "much of it," so the fact that it's the greatest amount doesn't mean that "much of it" also isn't unusable because of being in a remote location or being polluted.