Chemistry - GOC Question with Solution | TestHub

Down group 16 the conjugate-base anion gets larger, so the negative charge is spread over a larger volume and is better stabilised : $\mathrm{Te}{\mathrm{H}}^{-}$ $>$ $\mathrm{Se}{\mathrm{H}}^{-}$ $>$ $\mathrm{S}{\mathrm{H}}^{-}$ $>$ $\mathrm{O}{\mathrm{H}}^{-}$ in stability. The more stable the conjugate base, the stronger the acid, so acid strength is ${\mathrm{H}}_2\mathrm{O}$ $<$ ${\mathrm{H}}_2\mathrm{S}$ $<$ ${\mathrm{H}}_2\mathrm{Se}$ $<$ ${\mathrm{H}}_2\mathrm{Te}$. For atoms in the same group, size matters more than electronegativity.