The first and second ionization constants of $H_{2X}$ are $2.5 \times 10^{-8}$ and $1.0 \times 10^{-13}$ respectively. The concentration of $X^{2-}$ in $0.1$ M $H_{2}X$ solution is ____________\( \times 10^{-13}\) M. (Nearest Integer)
Method used for separation of mixture of products (B and C) obtained in the following reaction is: 