Hey Manjunath! As i have mentioned in other questions that JEE Mains is a national level entrance exam and it covers almost all the topics from 11th and 12th standard course book so all the topics are important and equall weightage is given to it. But some topics like Permutations and combination, Probability etc are some topics which are little tricky and difficult. Hope this may help you. 

Dear student, there can be many topics from mathematics from which tough questions can be asked, but the most frequent among them are -

• Complex Numbers – Easy to master, lot of lateral thinking involved.
• Permutation and combinations – Lot of cases to remember, and subsequent application also requires sharp, spontaneous thinking.
• Probability – Part of it is a direct extension of Permutation and Combination. Probability often seems like the easiest chapter that one can ace, but one should constantly be on the lookout for trick questions.

All the best 

Hope this helps