Find concentration of $\mathrm{X^{2-}}$ at equilibrium in 0.1 M $\mathrm{H_2X}$.
Given: $\mathrm{Ka_1} = 2.5 \times 10^{-7}$, $\mathrm{Ka_2} = 1 \times 10^{-13}$
(A) $2.5 \times 10^{-7}$
(B) $1 \times 10^{-13}$
(C) $6 \times 10^{-12}$
(D) $5 \times 10^{-10}$