"It is a room."
Translation:Det er et rum.
Could this also be translated "Det er et vaerelse" or does that not mean the same thing, for some reason?
They mean the same thing, and it is an accepted answer, though I think you'll receive a typo warning for writing æ as ae. I don't know why.
The difference between rum and værelse is that a rum can be any room, e.g. a conference room, a storage room, ie. any place enclosed by four walls inside a building. Værelse is more specific and refers to a room intended for people living there.
Since we do not have any context, both translations should be correct. Although, because of that, I guessed they were looking for rum rather than værelse.