Question

Why do some metals corrode whereas, some metals don't?

Answer 1

It depends on how reactive the metals are with rainwater or oxygen in the air.

Explanation:

For example, iron rusts in water or even in plain oxygen when given enough time.
Gold is a less reactive metal and (in its pure form) does not tarnish or rust at all.

Also, some metal alloys (like stainless steel) are made to not rust as easily.