Assertion- Saliva in the mouth has antimicrobial activity
Reason- Lysozyme in the saliva helps to break the bacterial cell wall.

The correct option is A Both assertion and reason are true and the reason is the correct explanation of the assertion
The salivary glands present in the mouth produce saliva. Saliva contains salivary amylase (enzyme that converts starch to maltose), lysozyme, electrolytes (act as buffering agents) and water (prevents drying of mouth).
Lysozyme is a naturally occurring enzyme that is abundant in the body secretions like tears, saliva, mucous, human milk. Lysozyme acts as an antibacterial agent that prevents infections. It functions as an antimicrobial agent by cleaving the peptidoglycan component of bacterial cell walls which eventually leads to the death of the bacteria. Additionally, saliva also contains thiocynate ions${\left(SCN\right]}^{-}$, which are also bacteriocidal in nature. Hence, the assertion is true and the reason is the correct explanation to the assertion.