Final Answer:
In the bloodstream, the immunoglobulin present in the greatest concentration is IgG. Option 4) is the answer.
Step-by-step explanation:
Immunoglobulins, also known as antibodies, play a vital role in the immune system. IgG is the most abundant immunoglobulin in the bloodstream, constituting about 75% of the total immunoglobulin pool. It is responsible for providing long-term immunity against bacterial and viral infections. IgM (Option 1) is the first antibody produced during an immune response, but it is present in lower concentrations compared to IgG. IgA (Option 2) is primarily found in mucosal secretions. IgD (Option 3) is present in small amounts and is primarily associated with the surface of B cells. IgE (Option 5) is involved in allergic reactions but is present in lower concentrations than IgG.
Option 4) IgG is the answer.