The correct answer is OPTION 1 --Relative Adverb

In the sentence "He doesn't like to stay at the guest house where his uncle is staying," the adverb "where" is a relative adverb.

A relative adverb introduces a relative clause and relates to a noun or pronoun in the main clause. In this case, "where" is a relative adverb that introduces the relative clause "where his uncle is staying." It provides additional information about the location of the guest house, explaining the place where he doesn't like to stay.

So, the function of "where" is to connect the two clauses and give more details about the place, making it a relative adverb in this context.