Which one of the following acts as a physiological barrier to the entry of microorganisms in human body?

Acid in the stomach, saliva in the mouth, and tears in the eyes all operate as physiological barriers to microbial growth.
This sort of immunity is known as innate immunity, and it is a non-specific type of defence that exists from birth.

Physical barriers include skin and the mucus coating of the epithelium lining the respiratory, gastrointestinal, and urogenital systems and Monocytes acts as cellular barrier.