What type of passive immunity is gained by injecting antibodies derived from the serum of infected individuals?

The type of passive immunity gained by injecting antibodies derived from the serum of infected individuals is indeed classified as artificially acquired passive immunity. This form of immunity occurs when antibodies are introduced into an individual from an external source, rather than being produced by the individual's own immune system.

In this case, the antibodies are obtained from the serum of individuals who have already fought off an infection, providing immediate protection against that specific pathogen to the recipient. This is particularly useful in situations where rapid immune response is needed, such as in cases of exposure to certain viral infections or toxins.

Natural immunity, in contrast, occurs when an individual is exposed to a pathogen and their own immune system responds by producing antibodies. Direct immunity is not a standard term used in immunology, and active immunity involves the generation of one's own immune response following infection or vaccination, leading to the development of memory cells for long-lasting protection.