Maximum body water is present:
**Core Concept**
The distribution of body water is a critical aspect of physiology, with varying proportions in different body compartments. The total body water (TBW) is approximately 60% of an individual's body weight, with a significant portion being intracellular.
**Why the Correct Answer is Right**
Intracellular fluid (ICF) accounts for approximately 2/3 of the total body water, making it the largest compartment. This is due to the high water content in cells, which is necessary for various cellular functions such as metabolism, transport, and temperature regulation. The high concentration of solutes in ICF, particularly sodium and potassium ions, helps to maintain the cell's osmotic balance.
**Why Each Wrong Option is Incorrect**
**Option A:** Incorrect because intracellular fluid is not the smallest compartment; it is the largest.
**Option B:** Incorrect because extracellular fluid (ECF) accounts for approximately 1/3 of the total body water, not the majority.
**Option C:** Incorrect because blood plasma is a component of extracellular fluid but not the largest compartment.
**Clinical Pearl / High-Yield Fact**
In clinical practice, it is essential to consider the distribution of body water when managing patients with dehydration, fluid overload, or electrolyte imbalances.
**Correct Answer: C. Extracellular fluid.