To find the mass of BaSO4 formed, we first need to calculate the amount of BaCl2 reacted and then use stoichiometry to determine the mass of BaSO4 produced.

Calculate the mass of BaCl2 reacted:
Given:
Mass of BaCl2 = 285g
Mass percent of BaCl2 in the solution = 10%

Mass of BaCl2 reacted = (10/100) * 285g = 28.5g

Calculate the moles of BaCl2 reacted:
Molar mass of BaCl2 = 137.33g/mol + 2(35.453g/mol) = 208.23g/mol

Moles of BaCl2 reacted = 28.5g / 208.23g/mol = 0.137 mol

Determine the mass of BaSO4 produced using stoichiometry:
Balanced chemical equation: BaCl2 + H2SO4 -> BaSO4 + 2HCl
Based on the equation, 1 mole of BaCl2 reacts to produce 1 mole of BaSO4.

Moles of BaSO4 formed = 0.137 mol

Molar mass of BaSO4 = 137.33g/mol + 32.06g/mol + 4(15.999g/mol) = 233.39g/mol

Mass of BaSO4 formed = 0.137 mol * 233.39g/mol ≈ 32g

Therefore, the mass of BaSO4 formed is approximately 32g.