Hello,



Though all the chapters are important but these are following chapters that are important for making a good base in class 12 :

Chemistry :

Chemical Bonding
Equilibrium
Basic Concepts of Organic Chemistry
Hydrocarbons
Physics :

Units and Vectors
Newton's Laws of Motion.
Work Energy Power
Rotational Dynamics
Waves and SHM
Mathematics :

Relations and Functions
Limits, continuity and differentiability
Trigonometry
Coordinate Geometry
Permutation and Combination
Binomial Theorem
Probability

I hope this helps.