Speed of violet light in vacuum

Explanation: Light travels at approximately 300,000 kilometers per second in a vacuum, which has a refractive index of 1.0, but it slows down to 225,000 kilometers per second in water (refractive index of 1.3; see Figure 2) and 200,000 kilometers per second in glass (refractive index of 1.5).

Answer: 300,000,000 metres per second

These waves all travel at the speed of light (300,000,000 metres per second) in a vacuum.