I want to refinish metal patio chairs that have rusted on the arm rest

steel wool works well for removing rust.

Rust removers, vinegar soak, brass or steel wire brush/hand or drill or grinder powered - wear goggles!

Then spray paint with rusty metal primer, then spray paint.

Vinegar might help.

No real problem. Scrape and sand all the rust off or until the metal is Smooth. Paint with a couple of coats of Rustoleum, and seal with a waterproof sealer. (Don't neglect the bottoms of any rails, arms, and feet.) If the chairs will be sitting on concrete or rocks, consider putting an inexpensive rug under the chairs. Best wishes 😇💖

You can spray paint them with Rustoleum from Walmart, it is made for cosmetic rust.

Use a wire brush to get all the loose rust off, then sand it down smoothly. Wipe clean to get all the debris and dust off. Spray paint with a good primer, then spray with paint. I would use Rustoleum brand.

Steel wool - 0000 or fine sandpaper should take it off.

Balled up pieces of clean foil also remove rust. My dad had a walker that looked pretty bad and I gave this a try. I was amazed how rust came off. Looked almost new when I was done.