Which of the following is an example of passive immunity?

The correct answer is Option (2) → Injection of preformed antibodies

Immunity is active when the host itself makes antibodies after meeting antigens, and passive when ready-made antibodies are given to the body. Passive immunity is used when a quick response is needed, as in tetanus or snakebite, where preformed antibodies are injected.

Option (1) Vaccination — Incorrect. In vaccination, antigenic proteins or weakened/inactivated pathogens are introduced, and the body makes its own antibodies. This gives active immunity.

Option (2) Injection of preformed antibodies — Correct. Injecting preformed antibodies, such as antitoxin in tetanus or antivenom after a snakebite, gives passive immunisation.

Option (3) Exposure to antigens — Incorrect. When a host is exposed to antigens, it produces antibodies itself. That is the definition of active immunity.

Option (4) Memory B and T-cells production — Incorrect. Memory B and T-cells are produced by the body after vaccination or infection. They belong to active, acquired immunity, not to passive immunity.

NCERT Extract:
Vaccination and Immunisation – “… The vaccines also generate memory – B and T-cells that recognise the pathogen quickly on subsequent exposure and overwhelm the invaders with a massive production of antibodies. If a person is infected with some deadly microbes to which quick immune response is required as in tetanus, we need to directly inject the preformed antibodies, or antitoxin (a preparation containing antibodies to the toxin). Even in cases of snakebites, the injection which is given to the patients, contain preformed antibodies against the snake venom. This type of immunisation is called passive immunisation.”