Consider two Group IV metal ions \( X^{2+} \) and \( Y^{2+} \).
A solution containing \( 0.01 \, \text{M} \, X^{2+} \) and \( 0.01 \, \text{M} \, Y^{2+} \) is saturated with \( H_2S \). The pH at which the metal sulphide \( YS \) will form as a precipitate is _______. (Nearest integer)
(Given: \( K_{sp}(XS) = 1 \times 10^{-22} \) at \( 25^\circ \text{C} \), \( K_{sp}(YS) = 4 \times 10^{-16} \) at \( 25^\circ \text{C} \), \( [H_2S] = 0.1 \, \text{M} \) in solution, \( K_{a1} \times K_{a2}(H_2S) = 1.0 \times 10^{-21} \), \( \log 2 = 0.30 \), \( \log 3 = 0.48 \), \( \log 5 = 0.70 \))
