Dear smart naif,
You cannot really say that a particular topic is important in IIT-JEE but here i am giving you some topics from Physics,Chemistry & Mathematics that are a little more scoring than the rest of the topics !!!
Physics:
1.Modern Physics(X-Rays,Photoelectric Effect,Atomic Physics)
2.Kinematics
3.Mechanics(Rotational Motion-More important)
4.Work,Power & Energy
5.Reflection & Refraction of Light(Optics-V.important)
Chemistry :
1.Atomic Structure
2.Properties of elements in the Periodic Table
3.Chemical Energetics
4.Rates of Chemical Reactions(Chemiical Kinetics)
5.Chemical Bonding(V.Important)
6.D & F block elements(Remember the reactions)
7.Co-ordination Chemistry
8.Organic Chemistry(Full-Highly Scoring)
9.Solutions & Thermodynamics(Scoring)
Mathematics :
1.Complex Numbers(Easy & Scoring)
2.3D Geometry(V.Easy & Highly Scoring)
3.Vectors
4.Matrices(V.Easy)
5.Circle,Parabola,Straight lines(Simple & Scoring)
6.Definite Integration(V.Easy & Scoring)
7.Probability
All the best !!
Hope this helped you dear....
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