JEE Main 2026 — 24 January, Morning Shift — Question 64

$\mathrm{XS}(\mathrm{s}) \rightleftharpoons \mathrm{X}^{+2}$ (aq.) $+\mathrm{S}^{2-}$ (aq.) For precipitation of XS(s) $\left[\mathrm{X}^{+2}\right]\left[\mathrm{S}^{2-}\right] \geq \mathrm{K}_{\mathrm{SP}}(\mathrm{XS})$ $\left[\mathrm{S}^{2-}\right] \geq \frac{1 \times 10^{-22}}{0.01}=10^{-20}$ $\mathrm{YS}(\mathrm{s}) \rightleftharpoons \mathrm{Y}^{+2}(\mathrm{aq})+\mathrm{S}^{2-}(\mathrm{aq})$ For precipitation of $\mathrm{YS}(\mathrm{s})$ $\left[\mathrm{Y}^{+2}\right]\left[\mathrm{S}^{2-}\right] \geq \mathrm{K}_{\mathrm{SP}}(\mathrm{YS})$ $\left[\mathrm{S}^{2-}\right] \geq \frac{4 \times 10^{-16}}{10^{-2}}=4 \times 10^{-14}$ Now, $\mathrm{H}_{2} \mathrm{~S}(\mathrm{aq}) \rightleftharpoons 2 \mathrm{H}^{+}(\mathrm{aq})+\mathrm{S}^{2-}(\mathrm{aq})$ $\frac{\left[\mathrm{S}^{2-}\right]\left[\mathrm{H}^{+}\right]^{2}}{\mathrm{H}_{2} \mathrm{~S}}=\mathrm{K}_{\mathrm{a}_{1}} \times \mathrm{K}_{\mathrm{a}_{2}}=1 \times 10^{-21}$ $\left[\mathrm{S}^{2-}\right]=\frac{1 \times 10^{-21} \times\left[\mathrm{H}_{2} \mathrm{~S}\right]}{\left[\mathrm{H}^{+}\right]^{2}} \geq 4 \times 10^{-14}$ $\left[\mathrm{H}^{+}\right]^{2} \leq \frac{1}{4} \times 10^{-7} \times 10^{-1}$ $\left[\mathrm{H}^{+}\right] \leq \frac{1}{2} \times 10^{-4} \Rightarrow \mathrm{pH} \geq 4.3$