To be honest there are no such easy chapters in JEE MAINS. First I would suggest you to start with NCERT 11TH Standard textbooks of Physics, Mathematics and Chemistry. 11th NCERT Textbooks are a base for JEE Mains. Then you can go for 12th Standard NCERT Textbooks of Physics, Mathematics and Chemistry. See I would suggest you to clear all your concepts. If your concepts are clear then you can almost solve every question. Practice Practice Practice everyday as only Practice helps. Also remember to pay attention to every subject equally as doing only one or two subjects can affect your marks. 

If you still have any queries feel free to ask in the comment section down below .