As you have not specified which exam you are talking about, assuming you are asking for NEET some important topics are-

1)Biology-Human Physiology, Diversity of Living Organisms, Genetics and Evolution, Biology and Human Welfare.

2)Chemistry-Thermodynamics, Equilibrium, Coordination Compounds, Different Solutions

3)Physics-Thermodynamics ,Motion of system of particles and rigid body, Optics, Electronic devices.

For more detailed information you can visit this link- https://medicine.careers360.com/articles/neet-chapter-wise-weightage-and-important-topics