1. The balls under the desk are some.

Question

2. There are some balls on the desk.

(#2 is correct, right? What about #1? Is it OK?)

Answer 1

#2 is correct grammar. #1 is not.
The articles "a", "some" and "the", occuring all alone, should never follow a form of the verb "to be". Such a statement conveys no information at all.