Which of the following products is an example of an isotonic solution?

• A. 5% NaCl hypertonic saline
• B. 0.9% NaCl intravenous saline
• C. 0.45% NaCl hypotonic saline
• D. Distilled water

Answer: (B)

Verified step by step guidance

1. Understand the concept of isotonic solutions: An isotonic solution has the same solute concentration as the inside of a cell, meaning it does not cause water to move into or out of the cell by osmosis.
2. Recognize that the typical solute concentration inside human cells is approximately 0.9% NaCl (sodium chloride) by weight, which is why 0.9% NaCl solution is considered isotonic.
3. Compare the given options to this standard: 5% NaCl is much higher in solute concentration, making it hypertonic; 0.45% NaCl is lower, making it hypotonic; distilled water has no solutes, so it is also hypotonic.
4. Conclude that the 0.9% NaCl intravenous saline matches the solute concentration inside cells, so it is isotonic and will not cause cells to shrink or swell.
5. Remember that isotonic solutions are commonly used in medical settings to maintain fluid balance without disrupting cell integrity.