Which combination of optical properties is associated with crystalline lipids?

• A. Isotropic and birefringent
• B. Isotropic only
• C. Anisotropic
• D. Birefringent only

Answer: (A)

Crystalline lipids have an ordered, direction-dependent arrangement that makes their optical properties vary with direction. This directional dependence is called anisotropy. When light enters such a material, it can travel at different speeds along different crystal axes, leading to birefringence, where a single ray splits into two rays with different refractive indices. An isotropic material has the same refractive index in all directions and would not show birefringence. Because crystalline lipids inherently exhibit this directional variation, anisotropy best describes their optical behavior, with birefrence as a manifestation of that anisotropy.