Question

How many colours comprise white light?
A) Infinite
B) Seven
C) Three
D) Fourteen

Answer 1

Hint: We all know that a rainbow consists of seven colors. These seven colours must be a part of the usual sunlight because that’s the source of light through which the rainbow is formed. Now if we focus the beams of all the colors of the rainbow on a single spot, the combination of all these colors will result in a beam of white light.

Complete answer:
Sir, Isaac Newton was the first one to show that by passing the white light through a prism it can be broken into its composite colours VIBGYOR. VIBGYOR stands for Violet, Indigo, Blue, Green, Yellow Orange and Red. He also showed that using another prism these colours can be reassembled.
Electromagnetic Radiation composed of evenly distributed frequencies in the visible range of spectrum appears white light to the human eye.
Even the sunlight is the perfect white light but due to the scattering of light it appears yellow light from Earth which means in vacuum sunlight will be visible as pure white light.
Thus, using a prism under the colour spectrum of the visible range it can be stated that white light comprises seven colours as stated by Newton in 1666.
Therefore the correct option is B. , i.e. white light comprises seven colours.

Additional Information:
In television screens, white light is produced using the colours Red, Green and Blue at full intensity. This process is known as additive mixing.
Visible white light can be made by using various colour combinations including Yellow and Blue, Red and Cyan amongst others.
Human eye responds to wavelengths 380 to 740 Nanometres.
Human eye is insensitive to Indigo's frequency and thus it becomes indistinguishable from blue and violet even for people with good vision.

Note: VIBGYOR is a really good abbreviation to memorize the colour of the rainbow, and hence the constituent colours of white light. VIBGYOR is in the order of decreasing frequency and increasing wavelength. With Violet having the highest frequency and shortest wavelength.