Why is `H_2S` less acidic than `H_2` Te ?

Explanation

Hydrides of oxygen family are weak acids and dissociates in aqueous solution to give `H_3 O^+` ions.
`H_2 E + H_2 O hArr H_3 O^+ + HE^(-) , E= 0 , S , Se, Te`
`HE^(-) + H_2 O hArr H_3 O^+ E^(2-)`
The acidic character of these hydrides is due to the ionic nature of the bond between group 16 element, E and H. As we more down the group the bond disociation enthalpy of E-H bond decreases and acidic character increases. Thus acidic character of these hydrides increases in the order,
`H_2 O lt H_2 S lt H_2 Se lt H_2 Te`