what are the two natural phenomenon for formation of rainbow

Due to dispersion of light and internal reflection, a rainbow can be observed in the sky.

 

Rainbow is caused by dispersion of sunlight by tiny water droplets present in the atmosphere. The water droplets act like small prisms. They refract and disperse the incident sunlight, then reflect it internally and finally refract it again when it comes out of the raindrop. Due to this different colours reach the observers eye.