Is in a verb or preposition?

Answer 1

The word in may be a preposition (in the house) or adverb (come in), and much more rarely an adjective or a noun. It can be part of an idiomatic verb (e.g. look in) but it is not used alone as a verb.

Answer 2

"In" can be both a preposition and an adverb. As a preposition, it shows position or location, while as an adverb, it often indicates location or direction.