Final answer:
Some gases in Earth's atmosphere exist as molecules, like a. nitrogen and b. oxygen, while others, like argon, exist as individual atoms.
Step-by-step explanation:
The Earth's atmosphere is a layered envelope of gases that surrounds the planet. Composed mainly of nitrogen and oxygen, with traces of other gases, it sustains life and influences climate. The atmosphere has distinct layers: troposphere, stratosphere, mesosphere, thermosphere, and exosphere. It plays a crucial role in weather, climate, and protecting life from solar radiation.
Thus, the gases in Earth's atmosphere can be classified into two groups: molecular gases and noble gases. Molecular gases, such as nitrogen (N2), oxygen (O2), and certain compounds like carbon dioxide (CO2), exist as molecules, which means they are composed of two or more atoms bonded together. On the other hand, noble gases like argon (Ar) exist as individual atoms.