Dear Govindaraj,

Here, the O atoms draw electrons away from Z atom and make it more positive. The Z atom, therefore, becomes more effective in withdrawing electron density. In turn, electrons of the H – O bond are drawn more strongly away from the H atom. The net effect makes it easier for the proton to dissociate and increases the acidity of the compound. With more number of 0 atoms bonded to Z, the compound becomes a stronger acid.

The acid strength is also explained by the oxidation number of central atom ( here P )

H3PO2  -      +1

H3PO3  -     +3

H3PO4  -     +5

The acid strength is also explained by counting the number of oxygen atoms bonded to P

hence order of acidity is : H3PO4   > H3PO3  >H3PO2

Please feel free to ask your queries here. We are all IITians and here to help you in your IIT JEE preparation.

All the best.

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