The index of refraction of a transparent material can be determined by:

The index of refraction is a fundamental property of materials that describes how light propagates through them. It is defined as the ratio of the speed of light in a vacuum to the speed of light in the material. To determine the index of refraction accurately, one method involves comparing the speed of light in air (which is very close to the speed of light in a vacuum) with the speed of light in the transparent material.

When you divide the speed of light in air (or vacuum) by the speed of light in the material, you obtain the index of refraction. This ratio provides insightful information about how much the light slows down as it enters the material, which in turn affects how light bends when it passes from air into that material.

This method is direct and relies on well-established principles of optics. The other choices do not reflect the correct relationship for determining the index of refraction, as they either mix concepts incorrectly or do not pertain to the calculation of refraction properly.