"None of the restaurants is independent."
Translation:Keine Restaurants sind unabhängig.
I would say that the English of this is "No restaurants are independent". "None of the restaurants" means that none in a particular group are independent, "no restaurants" says that there isn't a single one that is independent.
You're right. "None of the restaurants" would be "Keine der Restaurants" in German.
Wouldn't it be Keins der Restaurants ist unabhängig, to maintain the singular? In plural, I agree it would be Keine der Restaurants sind unabhängig.
Yes, It would be "Keins [oder "keines"] der Restaurants ist unabhängig."
No one would say "keine der Restaurants", it sounds very odd.
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?