The speed of light with the rise in the temperature of the medium

The speed of light in a medium depends on the optical properties of that medium, specifically its refractive index.

The speed of light in a medium is given by the relation:

v = c / n

where v is the speed of light in the medium, c is the speed of light in vacuum (approximately 3 × 10⁸ m/s), and n is the refractive index of the medium.

The speed of light in a vacuum is a fundamental constant of nature and does not depend on temperature, pressure, or any other physical condition.

However, in a material medium such as air, glass, or water, slight variations in the refractive index with temperature may cause negligible changes in the speed of light. These changes are so small that, for all practical and theoretical purposes, the speed of light remains unaltered with temperature variations.

Therefore, with the rise in temperature of the medium, the speed of light effectively remains unaltered.

Hence, the correct answer is Option C: remains unaltered.