Raj sells an apple. Is it correct?
A more apt Hindi translation for your sentence would be: राज एक सेब बेचता है।
It could be Raj sells the apple, no?
If it's apples and not apple, shouldn't it be हैं?
Here, 'है' refers to the subject 'Raj' (राज) and not to the object 'apples' (सेब). Since Raj is singular, usage of 'है' is apt here.
Isn't this also the Duolingo translation for "Raj sells the apple"?