Between glass and water, glass is considered a denser medium and water is a rarer medium.

Question

Accepted Answer

: Glass and water are compared by the speed of light in them, not by their physical density. The speed of light in glass (2.00 × 10⁸ m/s) is less than in water (2.25 × 10⁸ m/s), so glass is optically denser and water is optically rarer, regardless of their physical mass density.