A more idiomatic English translation would be "Are you okay?". "Are you fine?" is not technically wrong, it just sounds a little odd.
"Are you fine?" does not sound like native English, but the system won't let me report the English as unnatural, only the Hindi, which is weird, since that's the language I'm learning. Native speakers of English use "fine" in the answer, but not in the question.
In American English "are you ok" is the best answer, but "are you well" sounds perfectly idiomatic from a UK standpoint. "Are you fine" is understandable, just strange.
Did you spell it exactly like that? I don't think Duolingo accepts "u" as acceptable spelling of "you".
I always find it interesting when commentors reject Duo's translation as bad English. As a native speaker of American English "are you fine" sounds okay.