Final answer:
The medication used to reactivate acetylcholinesterase in cases of nerve agent poisoning, like the farmer's situation of insecticide exposure, is pralidoxime (C).
Step-by-step explanation:
The medication used to reactivate acetylcholinesterase in the treatment of nerve agent poisoning is pralidoxime (C). Atropine is used as an anticholinergic to manage the symptoms by blocking the muscarinic acetylcholine receptors. Pralidoxime acts to reactivate acetylcholinesterase that has been inhibited by organophosphorus compounds found in some insecticides, which leads to the accumulation of acetylcholine and continuous nerve impulse transmission. This can result in respiratory failure and other severe symptoms as seen in the patient, which necessitates prompt medical intervention.