Newton used prisms to?
a. support descartes thought that color was secondary
b. show that light was composed of different colored rays
c. prove that white light contained no colors except white
d. none of these

B. Show that light was composed of different colored rays

Explanation:

In the eighteenth century Isaac Newton found out that when a beam of light from the Sun, passes trhough a prism is decomposed in many different colors. He named this phenomenom as dispersion of light.

This phenomenom occurs when a beam of white light (which is compound of many wavelengths or "colors") is refracted (the different rays of light are diverted depending on their wavelengths) in some medium, leaving their constituent colors separated.