"In the apartment there is a bedroom, a bathroom and a kitchen."
Translation:W mieszkaniu jest sypialnia, łazienka i kuchnia.
I used "oraz" instead of "i" and I think it should be okay in this context.
We have "apartament" - it is a big luxurious flat (or a suite in an expensive hotel).
Not so simple, I'm afraid, as the endings also depend on how the root of a noun ends....
Take a look at: https://www.duolingo.com/comment/14379227 for commentary and pointers to various lists.
This answer might also help with your recent query under "Znasz tamtych studentów?".
btw I saw in the multiple choice there were 2 choices with są instead of jest but they had the wrong translations of bathroom and kitchen, but if it was like "w mieszkaniu są sypialnia, łazienka i kuchnia" would this be accepted?