Explanation

(c) Diamond sparkles more compared to ordinary glass, because of the phenomenon of total internal reflection of light, depending on the critical angle of the incidence of light in a material medium at its bounding surface with air.
The higher the refractive index of a transparent medium, the smaller is the critical angle and hence, the larger is the range of angles of incidence for more light to be totally reflected. A diamond has a large refractive index (2.417) and very small critical angle compared to say glass, hence diamond sparkles most.