What describes passive immunity?

Passive immunity is best described by the transfer of antibodies from one individual to another, which is exactly what occurs when antibodies are passed from mother to child. This form of immunity can happen during pregnancy when a mother’s antibodies cross the placenta to protect the fetus. After birth, antibodies can also be transferred through breast milk, providing immediate, though temporary, protection to the newborn.

This type of immunity is called "passive" because the recipient does not produce the antibodies themselves; they are received from another source. This is in contrast to other forms of immunity, such as active immunity, which involves the body's own immune response to an antigen, typically from vaccinations or natural exposure to pathogens. Thus, the correct answer highlights the specific mechanism of passive immunity through maternal transfer of antibodies.