Question

Acidity of diprotic acids in aqueous solutions increase in the order:

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Answer 1

The strength of acid is directly proportional to stability of its conjugated bases. With increase in the atomic size, the strength of the bond between hydrogen and the central atom decreases, and the Acidic strength of hydrides increases as the size of the central atom increases which weakens the $M-Hbond$.
Order of increasing size is $Te>Se>S$
And we also know that

$\text{Acidic nature}\propto \frac{1}{\text{Bond dissociation enthalpy}}$

$StoTe$ size increases, bond dissociation enthalpy decreases and acidic nature increases.
Thus acidic strength follows the order.

$H_{2}S<H_{2}Se<H_{2}Te$