The correct option is B Refraction
Monochromatic means light of a single wavelength or put simply, single colour. When light passes from one medium to another, it bends at certain angles and this property of light is known as refraction.
Here, the monochromatic light passing through the prism undergoes refraction and exactly the same incident light comes out. Dispersion can only occur if the incoming beam of light is polychromatic in nature.
Thus, he will be able to see only the refraction through the prism, not the dispersion or scattering.