Which of the following halogens does not form oxy-acids at room temperature?

F2 Cl2 Br2 I2

Cl2

Fluorine does not hove d-sub shell so it can only have one oxidation state. Therefore, it cann't form oxy-acids. Fluorine is the most electronegative element and always show −1 oxiadation state. In oxyacids, rest of the halogens have positive oxidation state.