Solubility of $BaSO_4 = 2.42 \times 10^{-3} \text{ g L}^{-1}$ Molar mass of $BaSO_4 = 233 \text{ g mol}^{-1}$ Molar solubility ($S$) $= \frac{2.42 \times 10^{-3} \text{ g L}^{-1}}{233 \text{ g mol}^{-1}} = 1.038 \times 10^{-5} \text{ mol L}^{-1}$ The dissociation of $BaSO_4$ is given by: $BaSO_4(s) \rightleftharpoons Ba^{2+}(aq) + SO_4^{2-}(aq)$ Here, $[Ba^{2+}] = S$ and $[SO_4^{2-}] = S$ The solubility product expression is: $K_{sp} = [Ba^{2+}][SO_4^{2-}] = S \times S = S^2$ $K_{sp} = (1.038 \times 10^{-5})^2 = 1.077 \times 10^{-10} \approx 1.08 \times 10^{-10} \text{ mol}^2 \text{ L}^{-2}$