It is the number of particles a molecule dissociates into when dissolved in a solvent.

• A. Osmoles
• B. Moles
• C. Molecules
• D. Ions

Answer: (A)

Osmoles measure how many particles a solute contributes when it dissolves, accounting for any dissociation into ions. This quantity reflects the actual number of osmotically active particles in solution, which depends on the van't Hoff factor (i): the number of particles formed per formula unit. For a non-dissociating substance like glucose, one mole yields one particle, while for a dissociating electrolyte like NaCl, one mole yields two particles (Na+ and Cl−), giving about two osmoles. That’s why osmoles best describe the situation described in the question: it specifically counts the particles produced by dissociation, unlike moles (amount of substance), molecules (untouched units), or ions (the products themselves).