Particle like behavior of light arises from the fact that each quanta of light has definite ...X... and a fixed value of ...Y.. just like a particle, Here, X and Y refer to

(4) Einstein arrived at the important result that the light quantum can also be associated with momentum $h\nu /c$. A definite value of energy as well as momentum is a strong sign that the light quantum can be associated with a particle. This particle was later named photon.