Calculate Na⁺ ions in Na₂SO₄ using molar mass, moles, and Avogadro's number

Steps:

• Molar mass of Na₂SO₄ = 2(23) + 32 + 4(16) = 142 g/mol.
• Moles of Na₂SO₄ = 30 / 142 ≈ 0.211 mol.
• Formula units = 0.211 × 6.02 × 10^{23} ≈ 1.27 × 10^{23}.
• Na⁺ ions = 2 × 1.27 × 10^{23} = 2.54 × 10^{23} (options imply ×10^{23}).

Why B is correct:

• Applies stoichiometry: 2 Na⁺ per Na₂SO₄ formula unit, times moles and Avogadro's number (6.02 × 10^{23} ions/mol).

Why the others are wrong:

• A: Assumes NaSO₄ (molar mass 119 g/mol), so 30/119 × 6.02 × 10^{23} ≈ 1.52 × 10^{23}.
• C: Equals Avogadro's number for 1 mol formula units, but 30 g is only 0.211 mol.
• D: Forgets to multiply by 2 (one Na⁺ per unit), so 0.211 × 6.02 × 10^{23} ≈ 1.27 × 10^{23} (rounded near 1.20 × 10^{23}).

Final answer: B