Is its an adjective

Answer 1

Yes, of a special type.

The word its (no apostrophe) is a possessive adjective(of or belonging to it) : e.g. its size is huge.

The word it's (apostrophe) is a contraction of the terms 'it is' or 'it has' : e.g. it's beginning to rain.

Answer 2

No. Oddly enough, the spelling its (without the apostrophe) is the possessive adjective, a pronoun.

The apostrophe version, it's, is a contraction for the words "it is."