## **Core Concept**
The core concept being tested here is the understanding of tonicity in intravenous (IV) fluids, specifically identifying which solution is hypertonic. A hypertonic solution has a higher concentration of solutes compared to another solution, in this case, human blood.

## **Why the Correct Answer is Right**
The correct answer, **D. 10% dextrose**, is hypertonic in nature. A 10% dextrose solution contains 10 grams of dextrose per 100 mL of solution. This concentration is significantly higher than the isotonic solutions commonly used, such as 0.9% saline or 5% dextrose. When administered intravenously, a 10% dextrose solution will have a higher osmotic pressure compared to blood, making it hypertonic.

## **Why Each Wrong Option is Incorrect**
- **Option A:** 0.9% NaCl is an isotonic solution, having the same osmotic pressure as blood. It does not cause a net movement of water into or out of cells and is therefore not hypertonic.
- **Option B:** 5% dextrose is also an isotonic solution when administered, as it initially has the same osmotic pressure as blood. Although dextrose is rapidly metabolized, at the time of administration, it is isotonic.
- **Option C:** 0.45% NaCl (half-normal saline) is hypotonic compared to blood. It has a lower solute concentration than blood and therefore would cause water to move into cells.

## **Clinical Pearl / High-Yield Fact**
A key point to remember is that hypertonic solutions, like 10% dextrose, can be used clinically to rapidly increase serum osmolality, which can be beneficial in certain conditions like severe hyponatremia. However, they must be used cautiously to avoid osmotic shifts that can lead to complications such as cerebral dehydration.

## **Correct Answer:** D. 10% dextrose.