Red is used as an emergency or danger signal as – (1) it is a striking colour (2) its wavelength is the longest (3) it is scattered (4) it has very high energy
(2) its wavelength is the longest Explanation: The effect of scattering is inversely related to the fourth power of the wavelength of a colour. Red has the highest wavelength of all the colours and is able to travel the longest distance through fog, rain, and the alike.