The concentration of ions in solution depends on the mole ratio between the dissolved substance and the cations and anions it forms in solution. Consider a compound that dissociates into cations and anions, the minimum concentration of each of those two products will be equal to the concentration of the original compound.
For example: Na2SO4(aq) → 2Na+ (aq) + SO2−4(aq)
The mole ratio between Na2SO4 and Na+ is 1:2, which means that 1 mole of the former will produce 2 moles of the latter in solution.
the concentration of the Na+ ions will be
1.0 M⋅ 2 moles Na+/1 mole Na2SO4 = 2.0 M