Final answer:
Condensation nuclei must be present for cloud formation, as they provide the particles around which water vapor can condense into liquid droplets, leading to cloud formation when combined with saturated air and cooling to the dew point.
Step-by-step explanation:
The statement that is true regarding cloud formation is that B. condensation nuclei must be present. For cloud formation to occur, conditions must favor the process of condensation, where water vapor cools and changes back into liquid droplets. These liquid droplets gather around condensation nuclei, such as dust, pollen, or smoke particles in the atmosphere. If these nuclei are not present, condensation would be significantly inhibited, and cloud formation would be less likely. Additionally, the air must be cooled to the dew point, the temperature at which condensation occurs, and the air must be saturated with moisture for clouds to form.
Although evaporation contributes to the water cycle by providing water vapor to the atmosphere, it is not a direct requirement for the physical formation of a cloud at a given time. The air parcel does not necessarily have to be below the Lifted Condensation Level (LCL) for cloud formation; it must reach or surpass this level for clouds to typically form. Lastly, high relative humidity is generally necessary for cloud formation, not low relative humidity as stated in option E.