What is the antidote for a blood agent?

The antidote for a blood agent is amyl nitrate. Blood agents, such as cyanide, are highly toxic substances that interfere with the body's ability to utilize oxygen, which can lead to asphyxiation at the cellular level. Amyl nitrate works by converting hemoglobin to methemoglobin, which can then bind to cyanide ions and facilitate their elimination from the body. This reaction helps to counteract the effects of the blood agent and restore the body's ability to transport oxygen effectively.

Other substances listed, such as atropine, chlorine water, and ephedrine, do not serve as specific antidotes to blood agents. Atropine is primarily used as an antidote for nerve agents, while chlorine water is not relevant in the context of blood agents. Ephedrine, a bronchodilator, does not address the toxicological mechanisms of blood agents. Thus, amyl nitrate is recognized as the appropriate choice in neutralizing the effects of a blood agent.