Which of the following is considered an isotonic solution?

• A. A solution that contains only pure water
• B. A solution with a lower concentration of solutes than blood plasma
• C. A solution with the same osmotic pressure as blood plasma
• D. A solution with a higher concentration of solutes than blood plasma

Answer: (C)

Verified step by step guidance

1. Understand the concept of isotonic solutions: An isotonic solution has the same osmotic pressure as another solution, typically body fluids like blood plasma, meaning there is no net movement of water across a semipermeable membrane.
2. Recall that osmotic pressure depends on the concentration of solutes in a solution; solutions with equal solute concentrations have equal osmotic pressures.
3. Analyze the options: Pure water has no solutes and thus a lower osmotic pressure than blood plasma, making it hypotonic; a solution with lower solute concentration than blood plasma is also hypotonic; a solution with higher solute concentration is hypertonic.
4. Identify that the isotonic solution must have the same solute concentration and osmotic pressure as blood plasma, so water movement is balanced and cells maintain their shape.
5. Conclude that the correct choice is the solution with the same osmotic pressure as blood plasma, as this matches the definition of isotonic.