Dear Sandeep,

Photon, as you might already know. is the basic unit of light and every beam if light is made up of millions of energy packets or photos. The photons are always in motion and they in vacuum, they travel at a constant speed, which is denoted by c. Traditionally photons are supposed to be massless particles.  You might wonder, why despite having momentum and energy photons are considered massless. The rules governing , the massless and the massive are different. The fact is that light is both a wave and a particle at the same time and the energy of a photon isn't decided by its mass or velocity ,but is determined by f , its frequency : E=h f ( h is Planck's constant).

Thank You.