What corrodes iron?

Because oxygen ions attach to iron atoms to make iron oxide (a.k.a. rust).

Unfortunately yes. Iron , especially when wet and even more especially when in salt water, oxidises to form rust. This means that all iron and steel products (eg nails, bicycles, cars) and buildings...

All acids contain hydrogen plus ions and these ions react with almost everything because hydrogen only has 1 valence electron to use. The reaction causes iron or any thing else to weaken.

diet soda like Diet Coke or Diet Pepsi, maby Dr.Pepper but haven't tested it also Coke, Pepsi, Sprite, ect. will corrode it but much slower

Large amounts of oxygen, combined with dark magic, have been proven to make iron corrode quite quickly.