Answer: Option B, condensation.
Explanation: Clouds are created when vapor of water mixed in the air condensates (because of the lower temperatures and change in pressure) in tiny water drops and ice crystals suspended in the atmosphere, this water drops and ice crystals difract the light of the sun, and this why we see the clouds white. The process in which vapor of water is transformed into liquid water again (or any gas tath transforming into a liquid) is called condensation, so the right answer is B.