A beam of light consisting of red, green and blue colours is...

For Total internal reflection, (i > i_{\mathrm{c}}) so, (\sin i > \sin i_c) (\sin 45^{\circ} > \frac{1}{\mu}) $⇒ \mu = \sqrt{2}$ $⇒ \mu = 1.414$ Since $\mu$ of green and violet is greater than $1 . 414$, so they will undergo total internal reflection. But red colour will be refracted. So the prism will separate red colour from the green and blue colours.