Visible light, also known as white light, consists of a collection of component colours. These colours are often observed as light passes through a triangular prism. Upon passage through the prism, the white light is separated into its component colours - red, orange, yellow, green, blue and violet. The separation of visible light into its different colours is known as dispersion.

The colours of the spectrum observed on the screen are in the order:

The statement made by the student is incorrect. Positions marked 3 (yellow), and 5 (blue) are similar to the colour of gold metal and the colour of the sky respectively. The student is stating the nature of colours in reverse order.

ii. (a) The position marked 7 (violet) corresponds closely to the colour of brinjal. It is due to the solution of potassium permanganate which gives its violet colour.

(b) Danger or stop signal lights are red. So position 1 corresponds to this colour.

The primary reason why the colour red is used for danger signals is that red light is scattered the least by air molecules. The effect of scattering is inversely related to the fourth power of the wavelength of a colour. So red light can travel the longest distance through fog, rain, and the alike.