Which of the following is classified as a nerve agent?

Sarin (GB) is classified as a nerve agent because it is specifically designed to disrupt normal nerve function. Nerve agents work by inhibiting the enzyme acetylcholinesterase, leading to an accumulation of acetylcholine in the synapses. This accumulation causes continuous stimulation of muscles, glands, and the central nervous system, resulting in a variety of symptoms ranging from respiratory failure to convulsions.

In contrast, the other substances mentioned, such as mustard gas, phosgene oxime, and lewisite, are classified as blister agents or asphyxiants, which primarily cause damage through different mechanisms. Mustard gas is known for causing severe skin blisters and respiratory damage; phosgene oxime affects the skin and lungs leading to corrosive injuries; while lewisite is primarily a blister agent that affects the skin and respiratory system. Therefore, Sarin is distinctly identified as a nerve agent due to its specific biochemical action on the nervous system.