Final answer:
Intracellular fluid (ICF) makes up about 60% of total body water, or roughly two-thirds of the body fluid in humans. In lean individuals, ICF accounts for about 50% of body weight, providing us with the correct answer, which is 2/3.
Step-by-step explanation:
The question asks how much intracellular fluid makes up body fluid. Intracellular fluid (ICF), which is the fluid within cells, constitutes a majority of the water in the human body. According to data, the ICF makes up about 60 percent of the total water in a human body, reflecting a significant proportion of total body water content.
In lean persons, intracellular fluid accounts for about 50% of the body weight, while extracellular fluids, including interstitial fluid and blood plasma, represent about 20% of the body weight. Therefore, the correct answer to the question is d) 2/3, as the intracellular fluid makes up roughly two-thirds of the body fluid in humans.