Tracers are elements that
a. must be inert
b. are used in minute amounts in plants
c. must have a stable nucleus
d. have an unbalanced electrical charge
e. can be monitored through biochemical reactions

Tracers are defined as elements that can be monitored through biochemical reactions. This characteristic of tracers makes them useful for the exploration of the mechanism of chemical reactions by tracing the path that the they follow from reactants to products. A good number of complex biochemical reactions (e.g. photosynthesis) have been studied using tracers.

rising temperatures because when water vapor in the air is cooled, it condenses. it turns back into a liquid and attaches to dust particles in the air. these very small water droplets group together to form clouds