Which of the following is an example of an inorganic compound?

An inorganic compound is typically defined as a compound that does not primarily contain carbon-hydrogen (C-H) bonds. Oxygen (O2) is a molecular form of the element oxygen, which is considered an inorganic molecule. Unlike organic compounds, which include carbon-based molecules like methane, carbohydrates, and proteins, O2 does not contain any carbon atoms at all.

In the context of the other options, methane is a simple organic compound characterized by its carbon content. Carbohydrates are organic molecules made mostly of carbon, hydrogen, and oxygen, and proteins are complex organic molecules composed of amino acids, which also contain carbon. Therefore, oxygen stands out as a clear example of an inorganic compound due to its lack of carbon in its molecular structure.