Dear Aspirant,

In an examination like JEE there are nothing which can be give precedence over another. All the topics are important and questions can be asked from any topic that is a part of the syllabus. There are few important topics like electromagnetism, co-ordinate geometry, organic chemistry, etc. But these topics are important as they carry a lot more weight as compared to others but you can't get a good rank through these.

See complete syllabus here: https://engineering.careers360.com/articles/jee-main-syllabus

Hope this helps. Thank you.