When water vapor cools off and begins to clump back together into crystals, this is known as what?

Water vapor is the gaseous form of water in temperatures above 100 degrees Celsius (the boiling point of water). Once the temperature goes below 100 degrees Celsius, then water vapor reverts back to its liquid form and the process is called condensation. In extremes of temperatures such that when temperature goes below 0 degrees Celsius (the freezing point of water), water vapor can crystallize and form ice without condensing back to water first. This process is called deposition. 

Answer:

a. energy is absorbed in the reaction.

explanation:

if in a given reaction the energy of products is greater than the energy of reactants it means that reaction is endothermic and during the reaction, the energy is absorbed by reactants. in an endothermic reaction, the products have more stored chemical energy than the reactants. and in this reaction the reactants are more stable than products before the compounds with less energy are always more stable.