50 mL of 0.0010 mol/L barium chloride is mixed with 50 mL of 0.0020 mol/L sodium sulphate…

Step 1. After mixing. $[\text{Ba}^{2+}] = 5.0 \times 10^{-4}\ \text{mol/L}$ and $[\text{SO}_4^{2-}] = 1.0 \times 10^{-3}\ \text{mol/L}$.

Step 2. Qsp. $Q_{sp} = 5.0 \times 10^{-4} \times 1.0 \times 10^{-3} = 5.0 \times 10^{-7}$.

Step 3. Compare. $5.0 \times 10^{-7}$ is far larger than $1.1 \times 10^{-10}$.