Oxoacids of Halogens

Oxidation numbers of chlorine: $HOCl$ (+1), $HOClO$ (+3), $HOClO_2$ (+5), $HOClO_3$ (+7).
As the oxidation number of the central atom increases, the strength of the oxoacid also increases.
More oxygen atoms on chlorine pull electron density away from the O-H bond, so the proton is released more easily.
Also, the negative charge of the conjugate base is delocalised over more oxygen atoms: $ClO^- \lt ClO_2^- \lt ClO_3^- \lt ClO_4^-$ in stability.
A more stable conjugate base means a stronger acid.
Increasing acid strength: $HOCl \lt HOClO \lt HOClO_2 \lt HOClO_3$

Oxidation numbers of chlorine: HClO (+1), $HClO_2$ (+3), $HClO_3$ (+5), $HClO_4$ (+7).
As the oxidation number of the central atom increases, the number of oxygen atoms attached to it increases, and the O-H bond becomes more polar.
The conjugate bases are also stabilised more by the delocalisation of the negative charge over more oxygen atoms: $ClO^- \lt ClO_2^- \lt ClO_3^- \lt ClO_4^-$ in stability.
The more stable the conjugate base, the stronger the acid.
So the correct order of acid strength is $HClO \lt HClO_2 \lt HClO_3 \lt HClO_4$.