Colostrum secreted by mother is rich in:

IgA antibodies

The correct answer is Option (3) → IgA antibodies

Passive immunization refers to the administration of preformed antibodies directly into the body to provide immediate protection against specific pathogens or toxins. These antibodies are obtained from a donor who has already developed immunity to the target antigen. The injected antibodies provide temporary protection and do not stimulate the body's immune system to produce its own antibodies.

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.