The first and second ionization constants of a weak dibasic acid H_2 A are 8.1 × 10^-8 and 1.0 × 10^-13 respectively. 0.1 mol of H_2 A was dissolved…

The first and second ionization constants of a weak dibasic acid $\displaystyle \mathrm{H}_2 \mathrm{~A}$ are $\displaystyle 8.1 \times 10^{-8}$ and $\displaystyle 1.0 \times 10^{-13}$ respectively. $\displaystyle 0.1$ mol of $\displaystyle \mathrm{H}_2 \mathrm{~A}$ was dissolved in 1L of $\displaystyle 0.1$ M HCl solution. The concentration of $\displaystyle \mathrm{HA}^{-}$ in the resultant solution is :