The speed of light is the same in a vacuum and in air (under normal conditions). In both cases, light travels at approximately 299,792,458 meters per second, which is commonly rounded to 300,000 kilometers per second. This value is denoted by the symbol "c" and is considered a fundamental constant in physics.
In a vacuum, such as outer space, light propagates without any significant interactions or obstructions, allowing it to maintain its maximum speed. In air, light also travels at nearly the same speed, as air has a refractive index close to 1. However, the refractive index of air is slightly greater than 1, which means that light does travel slightly slower in air compared to a vacuum. The difference is generally negligible for most practical purposes unless extreme precision is required.
It's worth noting that the speed of light can vary when passing through other transparent materials, such as water, glass, or other mediums with different refractive indices. The refractive index of a material determines how much the speed of light is reduced as it passes through that material.