Why is water considered a pure substance and not a mixture?
a. water can be separated physically into hydrogen and oxygen.
b. water is not a pure substance. its a mixture.
c. water is clear.
d. water can be separated chemically into hydrogen and oxygen.

Three cards with holes are arranged in a straight line. a light is shined through the first card’s hole and travels through all three cards. what does this tell you about light rays? a) that light is reflected b) that light is refractive c) that light travels in a straight line d) that light does not travel in a straight line