Question

why are acids corrosive

Answer 1

So, when an acid comes in contact with a metal surface it undergoes de-protonation quite easily. Essentially, the metal-acid system forms a Redox couple. This oxidation of metals is the main cause for corrosion.

Answer 2

they don't corrode many metals because metal tend to lose rather than accept elements aluminium is one metal that reacts with bases but bases are highly corossive to the skin add other organic substances