General objective of this assignment is to Briefly Explain Quantum Mechanics. Not only was classical mechanics not successful in explaining motions at the speed of light, in addition, it could not explain the particular behavior of matter on the atomic level. Quantum mechanics needs to analyze the behavior regarding molecules, atoms, and nuclei. Here also explain Blackbody radiation, Photoelectric effect, Compton scattering, Particle-wave duality and De Broglie waves.