Answer:
c the frequency.
Explanation:
Color is determined by frequency. When the frequency of the radiation is low, it is not visible. But as the frequency is increases , to somewhere around
400 Tera Hertz , color perception increases gradually from red towards violet.
Conversely , as the wavelength beginning from 400 nano meters and increases to about 700 nano meters , i.e from violet to red the colors of the visible light are clearly perceived by the eye.
