Which of the following types of chains are present in the structure of an antibody?

Immature lymphocytes differentiate in which of the following organs?

Passive immunity is obtained through the introduction of which of the following?

Identify the correct statements from the following:
$(i)$ The skin is the main physical barrier.
$(ii)$ Mucus coating of the epithelium lining the respiratory,gastrointestinal,and urogenital tracts is a physiological barrier.
$(iii)$ $IgA, IgM, IgE, IgG$ are types of $T$-cells.
$(iv)$ The primary immune response is very intense.

Define the following terms: Allergy and Cell-mediated immunity.

$NK$ cells are which type of cells?