Which solution has the highest osmolarity?

To determine which solution has the highest osmolarity, it is essential to consider the dissociation of each solute in solution, as osmolarity is a measure of the total solute concentration, taking into account the number of particles into which a solute dissociates.

Calcium chloride (CaCl₂) dissociates into three particles: one calcium ion (Ca²⁺) and two chloride ions (Cl⁻). Therefore, a 10 mM solution of CaCl₂ has an osmolarity of 30 mOsm/L (10 mM x 3).

Urea does not dissociate; it remains as a single particle in solution. Thus, a 10 mM urea solution has an osmolarity of 10 mOsm/L.

Glucose also does not dissociate in solution and will similarly contribute just one particle. Hence, a 20 mM solution of glucose has an osmolarity of 20 mOsm/L.

Sodium chloride (NaCl) dissociates into two particles: one sodium ion (Na⁺) and one chloride ion (Cl⁻). Therefore, a 120 mM solution of NaCl results in an osmolarity of