Which solute has the lowest molar concentration?
(A) 1.0 N HCl
(B) 0.4 N H₂SO₄
(C) 0.1 N Na₂CO₃
(D) 1.0 N NaOH

To determine the solute with the lowest molar concentration, we need to compare the normality (N) of each solution. Normality is a measure of concentration, specifically the concentration of equivalents of solute per liter of solution.

Let's calculate the molar concentration for each option:

(A) 1.0N HCl: HCl is a strong acid, so it dissociates completely in solution. 1.0N HCl means there is 1 mole of HCl per liter of solution.
(B) 0.4N H2SO4: H2SO4 is a strong acid and each mole produces 2 equivalents of H+, so 0.4N H2SO4 means there are 0.4 moles of H2SO4 per liter of solution.
(C) 0.1N Na2CO3: Na2CO3 dissociates into 2 Na+ ions and 1 CO3^2- ion, so it has 0.1 moles of Na2CO3 per liter of solution.
(D) 1N NaOH: NaOH is a strong base, so it dissociates completely in solution. 1N NaOH means there is 1 mole of NaOH per liter of solution.

Comparing these, the lowest molar concentration is found in option (C) 0.1N Na2CO3. Therefore, the correct answer is (C) 0.1N Na2CO3.