"None of the restaurants is independent."
Translation:Keine Restaurants sind unabhängig.
Because it is genitive, and in genitive plural, der is the correct form of "the"
There is clearly a disconnect in the subject-verb agreement between German and English. The subject in English is singular (hence the verb form "is"). The German offered by Duo translates into English as "No restaurants are independent" which is not what the English says, that is the two sentences are not identical. So why is "Keines der Restairants ist..." incorrect?