Why does H₂Se have a bigger Ka2 than H₂Te
The following data are from the Rubber Book (CRC Handbook of Chemistry and Physics), 89th edition, 2009, p 8-40. 

\begin{array}{lll}
\mathrm{acid} &amp; \mathrm{pK_{a1}} &amp; \mathrm{pK_{a2}} \\
\hline
\ce{H2S} &amp; 7.05 &amp; 19\\ 
\ce{H2Se} &amp; 3.89&amp; 11\\
\ce{H2Te} &amp; 2.6 &amp; 11\\
\end{array}

Note that $\mathrm{pK_{a1}}$ of $\ce{H2Te}$ was determined at 18 °C, all other data at 25 °C