Please help me. im very confused about this. why can acid cause an iron nail rust?

I don't quite understand this question but here we go. For anything made of iron to rust only two things need be present... Iron and Oxygen. Rust is also called Iron-Oxide meaning it consists of nothing but Iron particles that have bonded chemically with oxygen. Therefore an acid (depending on what sort of acid) can facilitate this reaction at an increased speed. For example putting a nail in soda (a highly acidic solution) will increase the rate of rust. Not mainly because of the acid but because of the Oxygen present in the soda. Any acid that contains oxygen or any oxidizing agent can cause a nail to rust very quickly. Any idea what sort of acid it is?