Which of these is true about pure substances?

a. they can only contain one type of atom
b. they can only contain one type of molecule
c. they may contain one type of atom or one type of molecule
d. they can contain different types of atoms and molecules

In order of decreasing light-transmitting capabilities of materials, which is the correct sequence? a. transparent -> translucent -> opaque b. opaque -> transparent -> translucent c. opaque -> translucent -> transparent d. translucent -> transparent -> opaque