Question

what is the speed of light in air ? does it remains constant or vary with time/place ?​

Answer 1

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It is a basic postulate of the theory of relativity that the speed of light is constant. This can be broken down into two parts: The speed of light is independent of the motion of the observer. The speed of light does not vary with time or place.

Answer 2

Answer:

Light in air is 1.0003 times slower than light in a vacuum, which slows it all the way down from 299,792,458 meters per second to 299,702,547 meters per second. That's a slowdown of 89,911 meters per second, which looks like a lot but is only three ten-thousandths of the speed of light.

Let's take a moment to look at what makes up the "air" in the Earth's atmosphere. The air is really a mixture of many different gases, and each gas has its own properties. The composition of air is not constant. It can vary from time to time and place to place.