Which one of the following facts is not true about passive immunity?

The correct answer is Option (1) → Colostrum provides active immunity

Note: The given answer is as per the official NTA Answer Key. However, the question can have more than one correct answer, i.e. both Option (1) and Option (4), because NCERT treats vaccination as active immunity, as explained below.

In passive immunity, ready-made antibodies are given to the body. In active immunity, the body makes its own antibodies when it is exposed to antigens, for example by infection or by a vaccine.

(1) Colostrum provides active immunity — Not true about passive immunity. Colostrum, the yellowish milk of the first days of lactation, has abundant antibodies (IgA). The baby receives them ready-made, so the immunity is passive.

(2) Antibodies are transferred from mother to foetus via placenta — True about passive immunity. The foetus gets some antibodies from the mother through the placenta, and this is passive immunity.

(3) Ready-made antibodies are directly given for protection against foreign agents — True about passive immunity. This is the definition of passive immunity. An antitoxin against tetanus and an antivenom after snakebite are examples.

(4) Vaccination is an example of passive immunization — Not true about passive immunity. A vaccine has antigens or a weakened pathogen, and the body makes its own antibodies and memory cells. This is active immunity. Passive immunisation is the injection of preformed antibodies.

NCERT Extract:
Active and Passive Immunity – “When ready-made antibodies are directly given to protect the body against foreign agents, it is called passive immunity. … The yellowish fluid colostrum secreted by mother during the initial days of lactation has abundant antibodies (IgA) to protect the infant. The foetus also receives some antibodies from their mother, through the placenta during pregnancy. These are some examples of passive immunity.”