The correct answer is C. Two.
A molecule of oxygen is made up of two oxygen atoms. The chemical formula for oxygen is O2. This means that there are two oxygen atoms in each molecule of oxygen.
The other options are incorrect because they do not represent the number of oxygen atoms in a molecule of oxygen. Option A states that there are four oxygen atoms in a molecule of oxygen. This is incorrect because there are only two oxygen atoms in a molecule of oxygen. Option B states that there are eight oxygen atoms in a molecule of oxygen. This is incorrect because there are only two oxygen atoms in a molecule of oxygen. Option D states that there are six oxygen atoms in a molecule of oxygen. This is incorrect because there are only two oxygen atoms in a molecule of oxygen.