Which of the following can have higher optical density but lower mass density?

Correct option is B

Correct Answer: (b) Turpentine
Explanation:
· Optical density depends on the refractive index, not the mass of the substance.
· Turpentine has a higher refractive index (~1.47–1.48) than water (1.33), meaning it has higher optical density.
· But its mass density (~0.87 g/cm³) is lower than water (1 g/cm³).
· Hence, turpentine is a classic example of higher optical density but lower mass density.
Information Booster:
· Optical density ↑ → Light slows down more in that medium.
· Mass density ↑/↓ has no direct relation with optical density.
· Refractive index is the key determinant of optical density.
Additional Knowledge:
· Water (a): Has lower optical density (n = 1.33) compared to turpentine; mass density is higher.
· Germanium (c): Very high optical density (n ≈ 4) and very high mass density — does not satisfy the condition.
· Glass (d): High optical density (n ≈ 1.5) and higher mass density than water — not the correct example.