Question

Why does 1 molar of NaCl have more osmotically active particle per liter of solution than 1 Osmolar NaCl?

Answer 1

1 mol/L NaCl corresponds to an osmolarity of 2 osmol/L. The NaCl salt particle dissociates fully in water to become two separate particles: an Na+ ion and a Cl− ion. Therefore, each mole of NaCl becomes two osmoles in solution, one mole of Na+ and one mole of Cl−
This is why 1 molar NaCl has actually 2 mol of particles (1 mol of Na+ and 1 mol of Cl-)but 1 Osmolar NaCl has only 1 mol of particle (0.5 mol of Na+ and 0.5 mol of Cl-).
1 molar of NaCl have more osmotically active particle per liter of solution than 1 Osmolar NaCl