once you remove the rust, if it is from a chip in the chrome itself, it will reappear in short order. To stave that off a bit longer, a light coat of a clear gloss like krylon will seal the chip from air. If it is a large area, "chrome-colored" paint would look less-bad...well, better than rust that is.
You need to seal it from air/moisture. No, wax won't do that.
neither (paint nor clear gloss) will last forever but it will slow it down from re-appearing and either beats re-chroming the entire bumper.