National League for Nursing (NLN PAX) Practice Exam

At room temperature, which of the following exists as diatomic molecules?

1. Carbon dioxide.

2. Oxygen.

3. Methane.

4. Argon.

The correct answer is: Oxygen.

Oxygen exists as diatomic molecules (O₂) at room temperature because it naturally pairs with another oxygen atom to form a stable molecule. In its gaseous state, oxygen is commonly found as O₂, which is essential for supporting combustion and respiration in living organisms. The diatomic nature is a characteristic of several non-metal gases, which tend to bond with themselves to achieve stability through the formation of covalent bonds. Carbon dioxide is comprised of one carbon atom and two oxygen atoms (CO₂), making it a triatomic molecule. Methane (CH₄) consists of one carbon atom bonded to four hydrogen atoms, and thus is also not diatomic. Argon is a noble gas that exists as monoatomic (Ar) under standard conditions, as it does not readily form bonds with other atoms. Therefore, among the options presented, oxygen is the only element that consistently forms diatomic molecules at room temperature.