Here's why:
* Pronouns replace nouns. Examples: he, she, it, they, we, you, I, this, that, these, those.
* "No" is an adverb. It modifies a verb, adjective, or another adverb. It expresses negation or refusal.
Examples:
* Pronoun: "She went to the store." ("She" replaces the noun "girl")
* Adverb: "No, I don't want to go." ("No" modifies the verb "want")