bx-zone.com says :-
All big structures have a robust foundation and so do all achievements. How well you do in IIT JEE mains and advanced exams totally depends on how early you start and how strong your foundation is. This principle applies in all three subjects Physics, Chemistry, and Mathematics but in Chemistry this principle applies more. Chemistry is the subject that is about studying the properties of the substances, the characteristics of elements, how compounds are formed from elements, the changes the substances undergo, and many more. Class 9 chemistry deals with matter, atoms, and molecules. You will come across concepts like moles in class 9. You will have to study the constituents of matter in class 9 and all these concepts create a foundation that comes of great use in the IIT JEE preparation in classes 11 and 12. Chapter 1 in class 9 chemistry is about Matter in our surroundings in which you study concepts like particles of matter, states of matter, and evaporation. Then chapter 2 follows that brings you concepts of mixture, solution, components of a mixture, physical and chemical changes. In chapter 3, you come across the concepts of atoms and molecules, and like earlier I stated the mole concept. Finally, you study the structure of the atom in chapter 4 along with concepts like isotopes, valency, mass number, and atomic number. I reiterate that if you are in class 9 don’t study these concepts only to clear the exams as not having a good clarity of atoms, molecules, moles, atomic number can impair the effectiveness of the IIT JEE preparation in class 11 and class 12. Well, I suggest that you read the class 9 NCERT chemistry textbook in detail, write down the concepts in a notebook and label it as ‘to be referred again in class 11’. Two years down the line before you go to the first class of chemistry make sure you go through this notebook. This process will deeply help and the concepts of class 11 will automatically start sinking in. And, in case you want to buy any class 9 textbook then you can get it from the used bookstore of bx-zone.com at a low price. Also, you can easily sell your used class 9 textbooks to students living near you using the used bookstore.