Inside a glass prism, let $V_B$, $V_G$ and $V_R$ be the speeds of blue, green and red light. Which relation is correct?

1. Speed in a medium is $v = \dfrac{c}{\mu}$, so higher refractive index means lower speed. 2. In glass, refractive index is highest for blue (short wavelength) and lowest for red (long wavelength). 3. Therefore blue travels slowest and red fastest: $V_B < V_G < V_R$. 4. The equality option fails because $\mu$ varies with colour in a prism. _Source: Samacheer Kalvi (TN SCERT) Class 10 Science, Unit 2 Optics "Refraction of a Composite Light - Dispersion", p.24_