What is the molecular formula for oxygen gas?

• A. O2
• B. O3
• C. O4
• D. O5

Answer: (A)

Oxygen gas, which is the form of oxygen that is most commonly found in the environment and essential for life, consists of two oxygen atoms bonded together. This diatomic nature is represented by the molecular formula O2. Each molecule of oxygen gas therefore contains two oxygen atoms, which is why O2 is the correct molecular formula.

In contrast, the other options represent different forms of oxygen. O3, for instance, is ozone, which comprises three oxygen atoms and is found in the Earth's stratosphere. O4 and O5 do not correspond to any stable or commonly recognized molecular forms of oxygen under standard conditions. Thus, the correct representation of oxygen gas is indeed O2, as it accurately reflects its diatomic molecular structure typically encountered in nature.