The order is h3po2>h3po3>h3po4 all this happens because of cross conjugation of the lone pair of e of the oxygen atoms having hydrogen and the doubly bonded oxygen atom  ..

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Hello Aspirant,

The correct acidic strength order is H3PO2>H3PO3>H3PO4.

Hello aspirant

Order of acidic strength  ( acidic character) among H3PO4, H3PO3 and H3PO2 is

H3PO4 ( pka 2.1)  < H3PO3 ( pka 1.5) < H3PO2 ( pka 1.3)

The acidic character of oxyacids of same elements which is in different oxidation state increases with the increase if it's oxidation state. Also number of P - OH bond increases the acidity of species decreases