Which element has atomic number 8 and forms O2 used in respiration and O3 in the stratosphere?

Which element has atomic number 8 and forms O2 used in respiration and O3 in the stratosphere?

• A. Nitrogen
• B. Carbon
• C. Fluorine
• D. Oxygen

Answer: (D)

Oxygen has eight protons in its nucleus, so its atomic number is eight. In the air it mostly exists as a diatomic molecule, O2, which organisms use in cellular respiration to extract energy from nutrients. In the stratosphere, UV radiation can split O2 into individual oxygen atoms, which can then combine with other O2 to form ozone, O3. This ozone layer absorbs a large portion of the sun’s harmful ultraviolet radiation, protecting living things on Earth. The other elements listed have different atomic numbers and do not form these two atmospheric forms in the same way, so they don’t fit the description.

Oxygen has eight protons in its nucleus, so its atomic number is eight. In the air it mostly exists as a diatomic molecule, O2, which organisms use in cellular respiration to extract energy from nutrients. In the stratosphere, UV radiation can split O2 into individual oxygen atoms, which can then combine with other O2 to form ozone, O3. This ozone layer absorbs a large portion of the sun’s harmful ultraviolet radiation, protecting living things on Earth. The other elements listed have different atomic numbers and do not form these two atmospheric forms in the same way, so they don’t fit the description.