Aqueous mounting media have an index of refraction that is significantly below that of the tissue.

• A. Significantly Above
• B. Significantly Below
• C. Equal To
• D. Slightly Above

Answer: (B)

Index matching controls how much light scatters when it passes through tissues and the mounting medium. Tissue has a relatively high refractive index (about 1.50) due to its proteins and lipids. Aqueous mounting media are water-based, so their refractive index is around 1.33–1.40—significantly lower than tissue. This large mismatch increases light scattering at the tissue–mounting medium interface, reducing image clarity and resolution, especially at higher magnifications. That’s why aqueous mounting media are described as having an index well below the tissue’s. If the medium’s index were closer to tissue’s, optical quality would improve; if it were higher, there would still be a mismatch, but the key point is the notable difference that affects image quality in practice.