how get 400+ mark in keam and does ncert text problems for physics and chemistry and RD Sharma for maths is sufficient
No doubt, NCERT textbooks of Class 11 and 12 are best for preparation. Along with this, As you told about preparing from RD Sharma is also good. Best books for KEAM- Objective Physics by Arihant, Concepts of Physics by H C Verma, Complete Mathematics by MC Graw Hills, Organic and Inorganic Chemistry by O.P. Tandon.
Some important topics that you must cover-
Physics- Mechanics of Solid & Fluids, Heat & Thermodynamics, Principles of Communication Devices, Dual Nature of Matters & Radiations, Oscillations, Atomic Nucleus, Electromagnetic Waves, Optics.
Chemistry- Thermodynamics, Electrochemistry, Periodic properties, Kinetics, Chemical Equilibrium.
Maths- Probability, Vector, Matrices & Determinants, Functions, Three-Dimensional Geometrical System, Inverse Trigonometric Functions, Mathematical Reasoning.