The correct options are
B diamond is less stable than graphite
C when proper cut and polished, a diamond reflects light in an array of many colours
D Impure sample of diamond is often black and are used in abrasives
diamond has high refractive index. It is very hard due to its crystal. Impure form is used as abrasives. diamond when properly finished given array of light due to high refractive index. Diamond is metastable componud. Less stable than graphite.