You are asked to design a retroreflector using two mirrors that will reflect a laser beam by 180 degrees independent of the incident direction of the beam. What should be the angle between the two mirrors?

Which statement is the best definition of an atom? a) anything that has mass and occupies space. b) the smallest particle that has the properties of an element. c) a substance that cannot be broken down chemically into simpler substances. eliminate d) the smallest unit of a substance that exhibits all of the properties characteristic of that substance.