Under which theory of liability would a severely injured guest who allegedly slipped on some liquid on the floor in your restaurant file in his or her lawsuit?

Negligence

Explanation:

Under the theory of liability, a complainant can file a lawsuit on the basis of negligence, of which borders on the failure of one to exercise his or her legal obligation either by omission or commission.  

The guest who is severely injured after allegedly slipping on some liquid on the floor of my restaurant can file a lawsuit to hold me liable for his injury because of failure to ensure safety of guests in my restaurant.