The antigen present in the pathogen is
A. A specific protein involve metabolism
B. Polysaccharide synthesized by it in the host
C. A specific protein or polysaccharide present on its coat
D. None of the above

Hint:-The antigen-antibody reaction is a particular chemical interaction between the antibodies formed by white blood cells especially B cells and antigens during the immune reaction. The immune system acts in response to an attack by a foreign antigen. The antigens and antibodies merge via a pathway called agglutination.

Complete solution:
An antigen is any substance that induces antibodies to be produced against it by one's immune system. This means that the antigen is not recognized nor accepted by the immune system and is attempting to fight it off. An antigen can be a substance from the atmosphere, such as pollen, toxins chemical, bacteria, viruses. An antigen can also form inside the body. Antigens get "targeted" by antibodies. The antibody is said to match the antigen in a way that it will bind to it because of an adaptation of the antigen-binding fragment to an antibody. In most cases, only one particular antigen may respond to and bind an adapted antibody. In some cases, antibodies can cross-react and can bind more than one antigen. Antigens are proteins, peptides (amino acid chains), and polysaccharides (monosaccharide chains/simple sugars) that are considered to be a T-cell independent antigen.
Therefore the correct answer will be option (C).

Note:- Vaccines are examples of immunogenic antigens purposely administered to a patient to activate the adaptive immune system's memory mechanism for the antigens of the pathogen attacking the patient. Vaccines contain a harmless version of the virus or bacteria that causes the illness to which one is not immunized. Before being used in the vaccine, the bacteria or virus gets killed, weakened, or broken down into small pieces so that they can cause an immune reaction without getting one sick.