To find the solution with the most concentration, we multiply the given molarity of solution to the given volume and multiply each with the molar mass to get the mass of solute of each solution. For H2SO4, the mass of solute is 1.96 grams; for PbSO4, 1.515 grams; for H2O2, 0,714 grams and for NaCl, 58 grams. Hence the answer is NaCl.