Hello student,

According to me, OP Tandon is better chemistry book compared to RK Gupta as it starts from the very basics and has good conceptual questions too.

Also, you can choose any book to prepare for JEE Mains. More or less, all books teach you the same theory and then you have to practice a lot of questions on your own. If you have joined any coaching centers, then you just need to follow what they teach you and practice from the materials they give you. Nothing else. Please don’t refer to more than one book for any topic. I advise you select that one book for each topic at the earliest and start preparing as soon as possible. 

The marks you score depends only on the effort that you put for that particular subject and not completely on any books. So its difficult to suggest you about the marks you will score based on books.

Hope this will be helpful..