A part of speech that is used instead of a noun is called a pronoun.For example- Samiha is a good student. She goes to school every day. Here, She is the pronoun
Noun is any name of person, product, place, things etc. That means any naming word is known as noun. Noun works as a- i) Subject ii) Object iii) Complement iv) Completive and v) Appositive
Parts of Speech means parts of a sentence. Each and every word of a sentence is called parts of speech.