Which among the following has its refractive index closest to that of crown glass?

Options

A. Canada balsam
B. Sapphire
C. Diamond
D. Ruby

Answer

A

Explanation

Due to its high optical quality and the similarity of its refractive index to that of crown glass (n = 1.55), purified and filtered Canada balsam was traditionally used in optics as an invisible-when-dry glue for glass, such as lens elements