A prism ABC (with BC as a base) is placed in different orientations. A narrow beam of white light is incident on the prism as shown in the figure. In which of the following cases, after dispersion, the sixth color from the top corresponds to the color of the sun?

In case II, after dispersion, the sixth colour from the top corresponds to the colour of the sun.
When we pass white light with an ideal orientation of the prism of base BC then we get the following light spectrum of different colours of white light.
 

We can observe the sequence of the spectrum that is not in the correct order as mentioned in the question. For Example, according to the question, in the spectrum of sunlight, orange should have been at sixth from the top, but in the above situation, it is not oriented as such.

Therefore, we have to revert the prism and then we will find the required spectrum of sunlight, described above.

Hence, "II" is the correct option.