Question

how rainbows are formed in the sky explain

Answer 1

Rainbow is formed by total internal reflection of water droplet.
It is form opposite to the sun.
Rainbow form circular.
but due to Horizon it looks semicircular. but due to Horizon it looks semicircular

Answer 2

rainbows are formed by the dispersion of light
in which a prism is used to disperse white light into seven colour of light
in rainbow water droplets present in atmosphere act as a prism . when white light falls on water droplet it disperse light into seven colours
hope it helps you