Final answer:
Mannitol is the intravenous drug used to reduce intracranial pressure during a craniotomy because it is an osmotic diuretic that decreases the fluid volume in the brain.
Step-by-step explanation:
The intravenous drug used to reduce intracranial pressure during a craniotomy is B. Mannitol. Mannitol is an osmotic diuretic that works by increasing fluid excretion in the kidneys, which in turn helps to reduce the volume of fluid in the brain, thereby decreasing intracranial pressure. Unlike other options like Sorbitol, Papaverine, and Epinephrine, Mannitol is specifically indicated for this purpose and is widely used in clinical settings for the management of cerebral edema and to improve the outcomes of neurosurgical procedures like craniotomies.