1. Oxygen (O2): Essential for respiration in most living organisms.

2. Nitrogen (N2): The most abundant gas in the Earth's atmosphere, used in fertilizers.

3. Carbon Dioxide (CO2): A greenhouse gas produced by respiration and burning fossil fuels.

4. Helium (He): A very light noble gas used in balloons and in MRI machines.

5. Methane (CH4): A powerful greenhouse gas produced by livestock and natural gas leaks.