Polymorpho-nuclear leukocytes (PMNL-neutrophils) belong to which type…

The correct answer is Option (2) → Cellular barriers

Innate immunity has four types of barriers. Certain white blood cells can phagocytose and destroy microbes; these cells form the cellular barriers. They include polymorpho-nuclear leukocytes (PMNL-neutrophils), monocytes and natural killer cells in the blood and macrophages in tissues.

Option (1) Physiological barriers — Incorrect. Physiological barriers are acid in the stomach, saliva in the mouth and tears from the eyes, which prevent microbial growth. They are secretions, not cells.

Option (2) Cellular barriers — Correct. PMNL-neutrophils are leukocytes that phagocytose and destroy microbes, so they form a cellular barrier.

Option (3) Cytokine barriers — Incorrect. Cytokine barriers are interferons, proteins secreted by virus-infected cells that protect non-infected cells from viral infection.

Option (4) Physical barriers — Incorrect. Physical barriers are the skin and the mucus coating of the epithelium lining the respiratory, gastrointestinal and urogenital tracts.

NCERT Extract:
Innate Immunity – “… (ii) Physiological barriers : Acid in the stomach, saliva in the mouth, tears from eyes–all prevent microbial growth. (iii) Cellular barriers : Certain types of leukocytes (WBC) of our body like polymorpho-nuclear leukocytes (PMNL-neutrophils) and monocytes and natural killer (type of lymphocytes) in the blood as well as macrophages in tissues can phagocytose and destroy microbes. (iv) Cytokine barriers : Virus-infected cells secrete proteins called interferons which protect non-infected cells from further viral infection.”