Rustoleum Rust Remover at Walmart, about $6
Works well with a toothbrush.
Elbow grease. Do not use it on aluminum, or let it sit.
If it turns alloy or aluminum black, it can be polished, but that's more work.

Chrome polish works once the rust is removed, but it's mildly abrasive, that's how it polishes.
If the metal under the rust has no chrome on it any more, you'll have to deal with that.
I use Testor's silver paint on some flips, just to hide the rust spots. It's not permanent.

OA is the best, but it's got its own procedures. They are here somewhere.

Chrome is treated by abrasives or chemicals. You have to decide which is best based on what's on/in/under the chrome.