A cut diamond shines brilliantly due to

Correct answer: (b) total internal reflection

Explanation

A cut diamond sparkles due to total internal reflection, where light striking a face beyond the critical angle is fully reflected inside.

Diamond's very high refractive index (about 2.42) gives a small critical angle, trapping light through many reflections before it exits.

Molecular structure or light absorption do not produce this brilliance, ruling them out.