Final answer:
In Earth's atmosphere, ozone, dust, and water vapor are commonly found. Iron is not typically found in its pure elemental state but may be present in dust particles. Ozone has a protective function against UV radiation, while water vapor is integral to the water cycle.
Step-by-step explanation:
The substances that exist in Earth's atmosphere include B) ozone, C) dust, and D) water vapor. Earth's atmosphere is a complex mixture of various gases, particles, and compounds. Ozone (03) is found in the stratospheric layer of the atmosphere, where it plays a critical role in protecting the biosphere from ultraviolet light. Dust particles are suspended in the atmosphere and can be transported across long distances by wind patterns. Water vapor is a natural part of the air we breathe and plays a key role in the water cycle, through processes like evaporation and condensation.As for A) iron, while iron exists on Earth, its natural form found in the atmosphere as a pure element is rather rare; however, iron compounds can be present in dust particles. The main answer to the student's question is that substances B (ozone), C (dust), and D (water vapor) exist in Earth's atmosphere.