"Why are you in the bathroom?"
Translation:Perché sei in bagno?
What is the difference between "in bagno" and "nel bagno"? I don't know when we use "in" and when use "nella"/"nel"/"nello"/...
you need the article in this case, in the bathroom. There are some instances when you don't. like in ufficio, I think you just have to memorise them
I used "Perchè sei tu nel bagno" (I know the accent is wrong), but was marked wrong over the sei form and told either "Perché siete nel bagno?" or "Perché sei in bagno?" are correct. What's my error?
It would be "perchè tu sei nel bagno". You don't use "sei tu" for "are you..?", it's "tu sei...?"
I used "gabinetto" for bathroom. Is that technically toilet or something like that?
I have friends and family in Italy, and I believe from those experiences, that gabinetto is used in less "formal" speech such as with family at home. Bagno is one step up, and the use of the French "toilette" shoes how classy and polite you are. So gabinetto IS correct, even though duolingo days no.
I sincerely hope I'm not going to have to explain my No.2 to anyone whilst in the act.