In the rain is a prepositional phrase
It is a noun.
The word "rain" can be a noun or a verb. For example, in the sentence, "I like rain." it is a noun. In the sentence "It is going to rain." it is used as a verb.
Rainstorm is a noun. Nouns are people, places, and things.
In this sentence "it" is used as the subject of an impersonal verb and is therefore a pronoun.
part of speech
The part of speech for this particular word is a noun.
Rain is usually a noun, but can be a verb, as It's starting to rain.
what part of speech is beneath
adverb
what part of speech is work
the part of speech sashay is a averb
Did is a verb, and not is an adverb. Didn't is not any part of speech. It's a contraction of did and not.