Which of the following statements about mannitol is true?

Mannitol is classified as an osmotic diuretic, which is the key reason why the statement identifying it as such is true. Osmotic diuretics function by increasing the osmolarity of the blood and renal tubules, leading to the reabsorption of water into the vascular system and increasing urine output. Mannitol is effective in reducing intracranial pressure and managing cerebral edema because it pulls water out of cells and into extracellular spaces, which can then be excreted as urine.

In contrast, potassium-sparing diuretics, hyperkalemia, and sodium retention relate to other mechanisms and drug classifications. Mannitol does not work by sparing potassium; rather, it typically promotes the excretion of various electrolytes, including sodium. Thus, it would not lead to conditions like hyperkalemia or increased sodium retention in the body. The mechanism of action and usages of mannitol reinforce why identifying it as an osmotic diuretic is accurate.