What is the approximate refractive index of air?

Question 89 asks: "What is the approximate refractive index of air?"

The refractive index of a medium describes how fast light travels through it. For a vacuum, the refractive index is exactly 1. Air is a very thin medium, so its refractive index is very close to that of a vacuum, but slightly greater than 1.

Let's evaluate the given options:

• (A) 1.0003: This value is very close to 1 and is the commonly accepted approximate refractive index for air under standard conditions.
• (C) 7.52: This value is much too high for the refractive index of air. Such high values are typically found in very dense materials, not gases.

Therefore, the approximate refractive index of air is 1.0003.

The final answer is $\boxed{\text{A}}$