The correct option is D Cl2O7
Oxides of metals are basic in nature & oxides of non-metals are acidic in nature whereas the oxides of metalloids are amphoteric in nature.
Non-metallic character increases as we move from left to right in the periodic table so the acidic nature of their oxides will also increase. The acidic nature also depends upon the oxidation state. Hence, greater the oxidation state, greater will be the acidic character. Therefore Cl2O7 is the most acidic oxide.