Choice A rationale Heart rate is an important vital sign to monitor in patients, but it is not the primary outcome data to prioritize when administering a 20% mannitol intravenous (IV) solution. Mannitol is a diuretic that works by increasing the amount of urine produced. Therefore, while heart rate can be affected by fluid balance changes, it is not the most directly relevant outcome to monitor in this context. Choice B rationale Ankle circumference could be an indicator of peripheral edema, which might suggest fluid overload or poor kidney function. However, in the context of mannitol administration, which is a diuretic and would be expected to decrease fluid overload, ankle circumference is not the primary outcome to monitor. Choice C rationale Urinary output is the correct answer. Mannitol is an osmotic diuretic that increases urine production. It is used to reduce intracranial and intraocular pressure by drawing water out of tissues and into the bloodstream, from where it can be excreted by the kidneys. Therefore, urinary output is the most direct measure of its effectiveness and is the key outcome that should be monitored. Choice D rationale Dietary intake is always important to monitor in patients, especially those receiving IV therapy, as it can impact electrolyte balance and overall health status. However, it is not the primary outcome to monitor when administering mannitol.