Statement I : Diamond is very bright. Statement I : Diamond has very low refractive index.

Statement I is true as diamonds are renowned for their brilliance and brightness, which is a result of their unique optical properties [1]. Statement II is false because diamonds actually possess a very high refractive index of approximately 2.42, rather than a low one [1]. This high refractive index is critical to the diamond's brightness; it causes light to bend significantly upon entering the stone and facilitates total internal reflection [1]. When a diamond is properly cut, this high refractive index ensures that light entering through the top is reflected internally off the pavilion facets and returned to the eye, creating intense sparkle and brilliance [1]. Additionally, the high refractive index contributes to dispersion, or 'fire,' which splits white light into spectral colors [1]. Therefore, the brightness is a direct consequence of a high, not low, refractive index.

Sources

1. [1] Science , class X (NCERT 2025 ed.) > Chapter 9: Light – Reflection and Refraction > QUESTIONS > p. 150