Final answer:
The appropriate prefix for the oxygen atom in the chemical formula SO₂ is 'di-'. The compound is named 'sulfur dioxide'.
Step-by-step explanation:
The appropriate prefix that should be used for the oxygen atom when naming the chemical formula SO₂ is di-. According to the naming rules, the numerical prefix di- is used for the second element in the formula, which in this case is oxygen. So, the compound is named sulfur dioxide.