Dear gaotham reddy
For iit jeee there is no fixed weitage, it  vary from year to year...

If you see last 5 years paper topics from which most of the question asked is........

Maths:      
 calculus, Vectors, Complex numbers, co-ordinate geometry(2D+3D) Quadratic equations.


Physics:    
 Optics, Modern physics, Thermodynamics, A/C circuits, Fluid mechanics, Experiments.


Chemistry: 
Solid state, chemica bonding, Aldehydes, ketones, carboxylic acids, Alkenes, 
                alkynes, stereo and geometrical isomerism, transition elements, coordiantion compounds,
               electro chemistry, kinetics and equilibrium.


but I will suggest you to cover alll the topics and give more stress on above given topics.


Please feel free to post as many doubts on our discussion forum as you can. 
If you find any question Difficult to understand - 
post it here and we will get you the answer and detailed solution very quickly.
 We are all IITians and here to help you in your IIT JEE preparation. 

 All the best. 
 
Regards, 
Askiitians Experts 
Badiuddin