What is the concentration of sodium ions in 0.300 M Na₂SO₄?

Answer 1

Na₂SO₄ ==> 2Na⁺ + SO₄^2-

Note there are TWO Na⁺ ons for each Na₂SO₄

0.300 M Na₂SO₄ x 2 M Na⁺/1 Na₂SO₄ = 0.600 M Na⁺