1. Determine the moles of Na₂SO₄:

* Moles = Molarity x Volume (in liters)

* Moles Na₂SO₄ = 0.453 M x (42.0 mL / 1000 mL/L) = 0.01903 mol

2. Use the stoichiometry of the reaction:

* From the balanced net ionic equation, we see that 1 mole of Ba²⁺ reacts with 1 mole of SO₄²⁻ to form 1 mole of BaSO₄.

* Therefore, we need 0.01903 moles of BaCl₂ to react completely with the Na₂SO₄.

3. Calculate the volume of BaCl₂ solution:

* Volume = Moles / Molarity

* Volume BaCl₂ = 0.01903 mol / 0.131 M = 0.145 L

* Convert to milliliters: 0.145 L x 1000 mL/L = 145 mL

So, you need 145 mL of 0.131 M BaCl₂ to react completely with 42.0 mL of 0.453 M Na₂SO₄.