I have two questions-Which sentence is written correctly?

Es un buen clase.

Es un buena clase.
Es un buena clase.

I think it is Es un buen clase. Is that correct?
Second question-
The term pelota refers to any kind of sports ball. Pelota is a ball but what is confusing me is the "Sports ball" I would think it is true but I'm not sure

Once again, please refer to your later post, where I posted the answers.

Sra