Which of the following is the strongest acid?
More the % oxygen content, more the acidic nature.
The charge stabilization of oxyacids of chlorine increases in the order:
ClO−<ClO2− < ClO3− < ClO−4
which signifies that ClO− will have minimum stability and therefore, will have maximum attraction for H+. Thus, ClO− will be strongest base and so its conjugate acid HClO will be the weakest acid. Similarly, in this series ClO4− is the weakest base (maximum stabilized) and its conjugate acid HClO4 is the strongest acid.