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

An isotonic solution is one that has the same osmotic pressure as another solution, typically body fluids, which helps maintain cell integrity and fluid balance. Normal saline, composed of 0.9% sodium chloride in water, is classified as an isotonic solution because it closely matches the osmolarity of blood plasma. This characteristic allows it to be safely infused into patients without causing the cells to swell or shrink.

In contrast, distilled water is considered hypotonic because it lacks solutes, which can lead to fluid shifting into cells and potentially causing them to burst. Hypertonic saline has a higher concentration of solutes than body fluids, which can lead to cellular dehydration. A glucose solution, while it may have a similar concentration to plasma, does not have the same osmotic effect as saline solutions and is not classified as isotonic for all clinical applications. Thus, normal saline is the correct representation of an isotonic solution in this context.