"Who is in the city?"

Translation: Quis est in urbe?

[Alan_III]

Why is "Quis in urbe est" also accepted?

[Arnaud199221]

because "in urbe" is the ablative case of "urbs". I reckon that this is too advanced for the first skill so duolingo accepts the conjugation you used!

[HoroTanuki]

Why not "in oppido"?

[ItsJohnny_]

also Oppidum should be accepted since it is a synonym

[AmeliaG108223]

The word order doesn't matter as long as the conjugation is correct.

[AnaCG276850]

I dont understand difference in est and es

[Moopish]

est -> 'he/she/it is'

es -> 'You (singular) are'

Does that help?