Final answer:
The best sign to monitor in a known alcoholic undergoing withdrawal is mental status, as it reflects the acute symptoms of alcohol withdrawal that affect consciousness and behavior control.
Step-by-step explanation:
When monitoring a known alcoholic undergoing withdrawal from alcohol, the best sign to monitor would be his mental status. Withdrawal from alcohol can lead to serious changes in a person's consciousness and behavior control, and medically, it is crucial to observe any signs of confusion, agitation, or sedation that might signal complications in the withdrawal process. Medications such as propranolol, used for blood pressure control or anxiety; lactulose, which affects stool consistency as a part of hepatic encephalopathy management; and allopurinol, for reducing serum uric acid levels, while important, are not as immediate in indicating the acute symptoms of withdrawal as monitoring mental status.