**Core Concept**
The extracellular fluid (ECF) volume in adults is a critical component of fluid balance and is estimated based on body weight, age, and sex. The ECF is divided into intravascular and interstitial compartments, and its volume is influenced by various factors, including hydration status, blood pressure, and cardiac output.

**Why the Correct Answer is Right**
The ECF volume in an adult man weighing 70 kg is approximately 42% of his body weight. This is based on the average ECF volume of 70-80% in newborns, which decreases to 20-25% by adulthood. For a 70 kg man, this translates to approximately 14.6-16.5 liters of ECF. The correct option should be close to this estimated value. The ECF volume is essential for maintaining blood pressure, regulating electrolyte balance, and facilitating the exchange of nutrients and waste products between the bloodstream and cells.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is likely too low, as it would be below the estimated ECF volume for a 70 kg man.
**Option B:** This option might be close, but it's essential to consider the normal range for ECF volume in adults.
**Option C:** This option is too high, exceeding the estimated ECF volume for a 70 kg man.

**Clinical Pearl / High-Yield Fact**
In clinical practice, it's crucial to recognize that the ECF volume can be altered in various conditions, such as dehydration, heart failure, and cirrhosis, which can lead to changes in blood pressure, electrolyte balance, and renal function.

**Correct Answer:** B. 16.