Question

The extent of deviation of ray light on passing through a glass prism depends on it colour light of red color is used for danger sign

Answer 1

To how much extent of distance you can see a colour depends upon its extent of deviation of white ray light through a glass prism or of the sunlight through the layers of atmosphere. Red colour deviates the most that is why it can be seen from a distance. Thus, can be seen from a distance and used a danger sign