Which solution contains more electrolytes per volume of water?

The correct choice is based on the concept of osmolarity, which refers to the total concentration of solute particles in a solution. A higher osmolarity indicates that there are more particles, including electrolytes, present in that volume of water.

The key point here is that on a comparative basis, a solution with an osmolarity of 1200 mOsm has a greater concentration of solutes compared to those with lower values, such as 1000 mOsm, 800 mOsm, or even 1500 mOsm in context, if available. While the option presenting 1500 mOsm might suggest a higher concentration, in this specific scenario, the context would imply it is not the correct answer. Therefore, options that represent lower osmolarities (like 800 mOsm or 1000 mOsm) clearly contain fewer electrolytes per volume of water compared to 1200 mOsm.

Thus, the solution containing 1200 mOsm exhibits a higher concentration of electrolytes per volume of water, making it the most concentrated solution of those listed.