Select the incorrect statements :

            I) It is possible to eliminate dispersion by combining two prism of same refracting angles but of

            different materials.

            II) The angular dispersion depends on refractive index of the material of the prism.

            III) A ray of white light shows no dispersion on emerging from a glass slab although there

            occurs dispersion inside the glass slab

            IV) The velocity of light inside the glass slab is same for all different colours