Why did it not accept "krant"? It marked it as wrong in place of "nieuwsblad"
You need to use the right article.
Why doesn't "De jongens lezen het krant" work? Is it because krant doesnt have the gender?
Yes, krant uses de, not het.
can't i say "Het jongens lezen de krant" here?
No, in plural "the" always translates to "de".
ohh bedankt! but sometimes we use "de" for singular, right?
Did you see this grammar explanation?