Final answer:
Immunity passed from mother to child through the placenta is called b) naturally acquired passive immunity, involving maternal IgG antibodies that protect the newborn.
Step-by-step explanation:
Immunity that is passed from mother to child through the placenta is known as naturally acquired passive immunity. This involves the transfer of IgG antibodies from the maternal circulation to the fetus via the placenta.
These antibodies confer immediate protection against infection and safeguard the newborn for the first few months of life. An example of this type of immunity is seen when an infant acquires antibodies through the mother's breast milk, specifically in the form of secretory IgA.