Which of the following is a chemical used by phagocytes to destroy ingested foreign substances?

Hydrogen peroxide is a chemical that plays a crucial role in the immune response of phagocytes, which are cells that engulf and digest foreign particles such as bacteria and debris. When phagocytes encounter pathogens, they utilize various reactive oxygen species (ROS) to initiate a process known as the oxidative burst. During this process, hydrogen peroxide is produced as a byproduct, and it serves as a potent antimicrobial agent.

The action of hydrogen peroxide involves generating free radicals that can damage cellular components of the ingested microorganisms, including lipids, proteins, and nucleic acids, ultimately leading to their destruction. This effectiveness makes hydrogen peroxide an important tool for phagocytes in their role as part of the innate immune system, where quick and decisive elimination of potential threats is critical.

Other substances listed, such as nitric acid and lactic acid, do not serve the same function in the immune response, and even though superoxide anion is a reactive species produced by phagocytes, hydrogen peroxide specifically is a key factor in the bacterial killing process. Thus, hydrogen peroxide is recognized as a significant chemical utilized by phagocytes to neutralize and eliminate foreign substances.