Frankly speaking, every single topic is important and any of them is not skippable as every year competition is increasing.I am mentioning the top most important chapters name, but still i would recommend you to cover each and every topic.

• OSCILLATION
• MAGNETISM
• ELECTRONIC DEVICES
• KINEMATICS
• CURRENT ELECTRICITY
• HEAT AND THERMODYNAMICS
• ELECTROSTATICS
• LAWS OF MOTION
• OPTICS
• ELECTROMAGNETIC INDUCTION
• ATOMS AND NUCLEI
• DUAL NATURE OF MATTER
• ROTATIONAL MECHANICS

There are some chapter which are comparatively easier than the others and you can prepare those chapters giving less amount of time.
Those chapters are:-

• Optics( Mainly Ray Optics)
• Modern physics
• EM waves
• Electrostatics
• Current electricity
• Statics part of mechanics
• Simple Harmonic Motion
• Thermodynamics