1) whoever is correct ... "whoever gave it to you" is a noun clause. The whole noun clause is the object, not just the word "whoever". So the noun clause needs a subject...whoever, not whomever. Here's an example of "whomever": I'll return the tools to whomever you borrowed them from. (You borrowed the tools from s.o. = Direct object)

For this sentence, you would use whoever because you could answer the question with "he/she gave them" and not "him/her gave them".

whomever is more proper