Antibody found in yellowish fluid, colostrum is:

The correct answer is Option (4) → IgA

Colostrum is the yellowish milk produced in the first few days of lactation. It is rich in antibodies, mainly IgA, which protect the new-born infant. The baby receives these ready-made antibodies from the mother, so this is an example of passive immunity. In active immunity, the body makes its own antibodies.

(1) IgG — Incorrect. This is the main antibody in the blood. It can cross the placenta, so the foetus receives some of it before birth. It is not the antibody of colostrum.

(2) IgM — Incorrect. This is the large antibody that is formed first in an infection. It is not the antibody of colostrum.

(3) IgD — Incorrect. It is not the antibody of colostrum.

(4) IgA — Correct. It is the antibody of colostrum.

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.”
Active and 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.”