Question

modeling pure substances
not all molecules are compounds.

• oxygen (o₂) is a molecule of an element.
• hydrogen (h₂) is a molecule of an element.
• salt (nacl) is molecule of a compound.

why are the molecules of oxygen and hydrogen not compounds?

• they are made up of one type of element
• they are made up of two or more types of element
• they are not elements
• none of the above

Explanation:

Compounds consist of two or more different elements. Oxygen ($O_2$) and hydrogen ($H_2$) have only one - type of element.

Answer:

A. they are made up of one type of element