In which case will the osmolarity of two compartments equalize?

The osmolarity of two compartments will equalize when water moves to dilute the higher osmolarity side. This process occurs due to the principle of osmosis, where water moves across a selectively permeable membrane from a compartment with lower solute concentration (and thus lower osmolarity) to a compartment with higher solute concentration (higher osmolarity). The movement continues until the osmotic pressure is balanced, equalizing the osmolarity between the two compartments.

When the osmolarity is different, water aims to achieve a state of equilibrium. That means if one side has a higher concentration of solutes, water will preferentially move towards that area to dilute the solute concentration, effectively balancing the osmolarity across the membrane.

In the context of the other options, while solute movement through a semi-permeable membrane can affect osmolarity, it is not the primary mechanism through which osmolarity equalizes; rather, it is the movement of water that plays the crucial role. Furthermore, equal volumes do not necessarily dictate osmolarity because osmolarity depends on solute concentration, not just volume. When solutes are impermeable to a membrane, they cannot traverse it to balance the concentrations directly, which again highlights