How does an oxyacid with the formula XOn(OH)m change in strength as n increases?

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The structure of phosphorous acid, H3PO3. — oxyacid The structure of phosphorous acid, H₃PO₃.

For an oxyacid with the general formula ${XO}_{n} (OH)_{m}$ , the acid strength increases as the value of $n$ increases.1

This occurs because $n$ represents the number of oxygen atoms bonded to the central nonmetal atom that are not part of a hydroxyl ( $OH$ ) group. As $n$ increases, the oxidation number of the central atom also increases. A higher oxidation state for the central atom exerts a stronger electron-withdrawing effect, which polarizes the $O–H$ bond more effectively, facilitating the release of a hydrogen ion and thereby increasing the acid strength.1