EAMCET Engineering 2010 Solved Paper

As the size of central atom, (order of size O>S>Se>Te ) increases, the H−A (where A= central atom) bond length increases. Thus, the H−A bond dissociation energy decreases. Consequently H2 Te gives a proton (H+)more readily. Hence, it is most acidic among the given.
H2‌Te+H2O→H3O++HTe−