Which of the following pairs of light rays shows the widest separation in the spectrum of white light?

1. Analyze the question When white light passes through a prism, it splits into the spectrum (dispersion). The order, from least to most deviated, is:

Red, Orange, Yellow, Green, Blue, Indigo, Violet (ROYGBIV)

We need the pair of colours that are furthest apart in this spectrum.

2. Concept Different colours have different wavelengths, so they have different refractive indices in glass. Red has the longest wavelength and is bent the least. Violet has the shortest wavelength and is bent the most. The further apart two colours are in the ROYGBIV order, the wider their angular separation.

3. Solution Positions in the spectrum (1 = Red, 7 = Violet):

• A. Red (1) and Blue (5): gap of 4
• B. Orange (2) and Green (4): gap of 2
• C. Red (1) and Indigo (6): gap of 5
• D. Violet (7) and Green (4): gap of 3
• E. Yellow (3) and Red (1): gap of 2

The largest gap among the options is Red and Indigo, with a gap of 5 positions. Red and violet would be the absolute widest pair, but violet is not paired with red in any option.

4. Answer The correct option is C. Red and indigo.

5. Exam tip Write out ROYGBIV and number the colours 1 to 7 whenever you see a question like this. Then just subtract the positions. The pair with the biggest difference is the widest separated. Remember that red is bent least and violet is bent most.