Question

why don't we we write h and Cl only while writing the chemical formula for hydrogen chloride
why we write 2 with h and cl
why we write 2 before hcl​

Answer 1

hydrogen and chlorine or both diatomic molecules which required to atoms therefore it is represented by 2

hydrochloric acid is represented by 2 because to balance the chemical reaction we should ensure that it should follow the law of conservation of mass therefore it should be balanced