Which characteristic is associated with the most deadly chemical agents?

The characteristic associated with the most deadly chemical agents is extreme toxicity. This level of toxicity indicates that a chemical agent can cause severe harm or fatality even at very low concentrations. Agents with high toxicity can affect multiple systems within the human body, leading to rapid onset of symptoms and increased likelihood of fatal outcomes.

In contrast, while high boiling points and rapid evaporation can be relevant to certain chemical agents, they do not necessarily correlate with their lethality. For example, a chemical with a high boiling point might remain as a liquid at normal temperatures, which could make it less immediately hazardous in certain environments. Rapid evaporation may indicate that a substance could disperse quickly in the air, possibly increasing exposure risks, but it does not inherently make the agent more toxic. Wide availability does not correlate with lethality either, as some highly toxic agents may be restricted or closely regulated. Therefore, extreme toxicity stands out as the primary characteristic associated with the most deadly chemical agents, as it directly impacts the potential for harm to human health and safety.