The correct answer is Option (3)- Active immunity

Active immunity is the type of immunity that develops in a host when it is exposed to antigens, which can be in the form of living or dead microbes or other proteins. This process stimulates the production of antibodies within the host's body. Active immunity is characterized by its gradual onset and the time it takes to mount a full and effective immune response. It can be induced through deliberate immunization, where microbes are intentionally introduced into the body, or it can occur naturally when infectious organisms gain access to the body during an infection.

In contrast, passive immunity involves the direct administration of pre-formed antibodies to provide immediate protection against foreign agents. An example of passive immunity is the yellowish fluid called colostrum, which is secreted by a mother during the initial days of lactation. Colostrum contains abundant antibodies, particularly IgA, which serve to protect the infant. Additionally, during pregnancy, the fetus receives a supply of antibodies from the mother through the placenta. These instances exemplify passive immunity.

To summarize, active immunity is the immune response that develops when a host is exposed to antigens, while passive immunity involves the direct administration of pre-existing antibodies to provide immediate protection. Both active and passive immunity play crucial roles in defending the body against infections.

The innate immune system is the body's first line of defense against germs entering the body. It responds in the same way to all germs and foreign substances, which is why it is sometimes referred to as the "nonspecific" immune system.