I have two questions

1. whats the difference between a noun and a pronoun

2. whats the difference between physics and math and biology

Nouns are people, places, things, objects, those kind of things. Pronouns on the other hand, can replace the noun.

Examples of nouns;

Water park, dogs, books

Examples of pronouns:

I, you, we, us

Physics, if I am not mistaken, deal with all the behaviors and other related things about matter. Math deals with all the great numbers in life. Biology, as its name suggests, is the study of life, or the study of different living species and their behaviors.