Final answer:
The class of immunoglobulin with a half-life in the blood of 23 days is IgG.
Step-by-step explanation:
The class of immunoglobulin that has a half-life in the blood of 23 days is IgG.
IgG is a major antibody found in the blood and is responsible for fighting against diseases. It is the most specific for the antigen, making it an important component of the immune response.
It is worth noting that IgG is present in the blood in the highest concentration and is the main antibody of secondary responses.