I'm going to call out a friend in group chat about his ethics.
Why do you think you need to call him out?
He abuses our group chat too much and he doesn't study a lot, sometimes way less than I do. I can't take it anymore.
It sounds like you need to stick up for yourself and your other group members.  In this case, the group chat would be a perfect place to call your friends poor behavior out.  I hope he mends his ways!
That's great. I'm going to call him out tomorrow.
I suggest you to do it in a polite way. There is no point in calling him names and being rude about his behavior, it might escalate the problem and cause issues within the group.