Background Paragraph: You generally can’t see, smell, taste, hear, or feel radiation. Fortunately, there are devices such as Geiger counters that can detect radiation. A Geiger counter, like the one pictured in the Figure below , contains atoms of a gas that is ionized if it encounters radiation. When this happens, the gas atoms change to ions that can carry an electric current. The current causes the Geiger counter to click. The faster the clicks occur, the higher the level of radiation. 
Story: Steve is a geologist and is doing a study on the radioactivity of different rocks. He has gathered two distinctly different rocks for examination. The first rock is red in color, and the second is purple in color. He has brought along a Geiger counter to help him with his study. The red rock ends up making the Geiger counter click very rapidly, while the purple rock barely registers any clicks.
Is the purple rock more or less radioactive than the red rock? Is the red rock more or less radioactive than the purple rock? Which color rock is least likely radioactive? Which color rock is most likely radioactive?