Final answer:
The gas with the highest refractive index is not specified, but for gases the refractive index is generally close to 1. Although air has a refractive index of about 1.0003, the exact highest refractive index gas would depend on the specific type and conditions.
Step-by-step explanation:
The question is asking which gas has the highest refractive index. The refractive index (n) of a substance indicates how much the path of light is bent, or refracted, when entering the substance.
For gases, the indices of refraction are very close to that of a vacuum which is 1, making gases like air have an index of refraction very close to 1 (for example, air has a refractive index of approximately 1.0003).
It is important to note that the refractive index can vary with the wavelength of light, but generally for gases, n is close to 1.0. Methods like interferometry can provide the high precision necessary to measure these slight differences in refractive index amazingly well.
In summary, while air has a relatively low refractive index (1.0003), the exact gas with the highest refractive index is not specified. It would depend on the specific gas and conditions such as pressure and temperature. For strong refractive indices, materials like diamond have much higher values.