what is wave theory and particle theory of light ?.... pls explain it  in a easy way 

The wave theory of light says that light is essentially a transverse electromagnetic wave and propagates in space as wavefronts. Wave front construction is done by Huygen's construction under which a point in the primary wavefront acts as a source of the secondary wavefronts. And secondary wavefronts give rise to the next primary wavefront, that is how the wave propagates. It explains refraction, reflection, interference, diffraction, polarization and other electro-optic effects like Kerr Effect etc.

Particle theory of light says, light consists of discrete packets of energy called quantum. And energy of each quantum is directly proportional to the frequency of the light. It can explain reflection, refraction, blackbody radiation and photoelectric effect.