To determine the refractive index of air, we need to understand the concept of refractive index. The refractive index is a measure of how much light is bent (refracted) when it passes from one medium to another. It is defined as the ratio of the speed of light in a vacuum (or air) to the speed of light in the given medium.

Now, let's go through each option and explain why it is right or wrong:

A. <1: This option is incorrect. The refractive index of air is greater than 1. The speed of light in air is slightly slower than the speed of light in a vacuum, so the refractive index of air is slightly greater than 1.

B. >1: This option is correct. The refractive index of air is greater than 1. As mentioned earlier, the speed of light in air is slightly slower than the speed of light in a vacuum, resulting in a refractive index greater than 1.

C. =1: This option is incorrect. The refractive index of air is not equal to 1. As explained above, the refractive index of air is slightly greater than 1.

D. =0: This option is incorrect. The refractive index of air is not equal to 0. The refractive index of a medium is always a positive value and greater than 0.

The correct answer is:

B. >1