I have a 2" ball that has rust and I was going to buy a new one.But I hope to save this one if I can. I used it last year but I left it on all winter.

seriously....put it in a 2 liter of coke for a couple of days soaking and then scrub with tin foil soon as you get it out.  Cheap and without the chemicals.  Just the ball pretty cheap I guess if rusted too bad- but would assume you would rather just replace the nut and keep the ball.

Either use it as is, or take some steel wool or an sos pad. 

Use a product called winx. And or use some mild acid called nu hull. Work on yachts in Florida and it gets rust stains off anything as long as the chrome is still intact

The ball will still work fine with the rust otherwise a new ball isn't much and it will look the best

Lime Away, also removes rust, acid based toilet bowl cleaner (used this to get rust spots off a fiberglass hull), muriatic acid (used in pools) also works, just dilute with water.  You can find lots of stuff at any Home Depot that will take rust off or like someone stated, get a new one.

What does it hurt? Other than not being all shiny, there's nothing wrong with it. Now, if you think it keeps your trailer from being grounded to the vehicle and messes up the lights, you need to hook up the white wires in the plugs, they provide the ground, not the ball.

Same thing happened to me this winter.  I took a wire brush and brushed off what I could of the rust, then slapped a glob of grease on there.  Good as new.

Thanks guys for all the tips,the worst I can do is just buy a new one but, it is not too bad at all.I looked at it better after posting this and it is just surface rust. Thanks again!