Correct Option
An antigen is a substance, typically a protein or polysaccharide, that is recognized as foreign by the immune system. Its primary function is to stimulate the immune system to produce specific antibodies. These antigens are often components of pathogens like bacteria, viruses, or toxins, triggering a defensive immune response in the body.
Incorrect Options
Option (A) is incorrect. Antigens do not directly destroy harmful bacteria. Instead, they trigger the immune system to produce antibodies and activate immune cells, which then neutralize or eliminate pathogens.
Option (B) is incorrect. Substances used to treat poisoning are called antidotes, not antigens. Antigens are involved in immune responses.
Option (C) is incorrect. Substances that lower body temperature are known as antipyretics (e.g., paracetamol). Antigens do not have this function.