Which of the following agents is associated with delayed symptoms?

The agent associated with delayed symptoms is mustard gas. Mustard gas, a chemical warfare agent, is classified as a blister agent, and it may take hours or even days for the full symptoms to manifest after exposure. Initial contact might not prompt immediate severe reactions, and symptoms such as skin blistering, respiratory distress, and eye damage can develop later, making it particularly insidious. This delayed reaction complicates treatment and evacuation processes since individuals may initially appear unaffected.

In contrast, the other agents listed, such as sarin, tabun, and lewisite, are known for producing more immediate and acute symptoms following exposure. Sarin and tabun are nerve agents, which cause rapid paralysis and distress, leading to very fast onset of symptoms, typically within minutes. Lewisite, although it can also have delayed effects similar to mustard gas, presents symptoms more quickly than mustard gas.