A composite light consisting of red, green and blue colours is incidence on face AB of a glass prism. The blue light is just totally internally reflected at face AC as shown in. Then

 

 

Glass is dispersive and the refractive index μ of glass is related to wavelength $\lambda$ as

$\mu =A+\frac{B}{{\lambda }^2}$

where A and B are constants. Since  ${\lambda }_R>{\lambda }_G>{\lambda }_B, {\mu }_R<{\mu }_G<{\mu }_B$. Therefore, blue, light is deviated the most and red light is deviated the least. Since blue light is just totally internally reflected at face AC,

$\sin i_c =\frac{1}{{\mu }_B}$

where i_c is the critical angle for blue light. Since μ_R < μ_B and μ_G < μ_B , the critical angles for red and green lights are greater than that for blue light. Hence red and green light are incident on face AC at angles less than their respective critical angle. Therefore, they will not suffer total internal reflection at face AC and will emerge out from it  So the correct choice is (c).