Question

which of the following is a molecule?
○ oxygen gas (o₂)
○ neon (ne)
○ iron (fe)
○ sodium (na)

Explanation:

A molecule is a group of two or more atoms bonded together. Neon (Ne), Iron (Fe), and Sodium (Na) are single atoms (monatomic) as they are noble gas, metal, and metal respectively, existing as individual atoms. Oxygen gas ($O_2$) consists of two oxygen atoms bonded, so it is a molecule.

Answer:

A. Oxygen gas ($O_2$)