Which decontamination agent is known to react violently with liquid mustard agent?

The correct answer is STB, which stands for Super Tropical Bleach. This decontamination agent is specifically formulated to neutralize various chemical warfare agents, including liquid mustard gas. When STB comes into contact with mustard agent, it reacts vigorously, breaking down the chemical structure of the mustard agent and effectively rendering it less harmful. This property makes STB a preferred choice in chemical agent decontamination responses.

Other agents listed, such as water, chlorine, and alcohol, do not have the same effectiveness against mustard agents. Water, while useful for dilution, may not effectively neutralize the harmful properties of mustard agent and could potentially spread contamination. Chlorine can react with some chemicals but is not specifically designed for denaturing mustard agents and can produce toxic byproducts. Alcohol, while it may have some disinfecting properties, does not adequately neutralize the dangers of chemical agents like mustard gas. Hence, STB's unique formulation and reactivity with mustard agent distinguish it as the correct choice in this context.