Final answer:
Gram-negative bacteria are the most resistant to chemical biocides due to their outer envelope and efflux pumps.
Step-by-step explanation:
Gram-negative bacteria are the most resistant to chemical biocides compared to the other options listed. This is because Gram-negative bacteria have a relatively thin cell wall composed of a few layers of peptidoglycan, surrounded by an outer envelope containing lipopolysaccharides (LPS) and lipoproteins. The outer envelope acts as a barrier, making it more difficult for chemical biocides to penetrate and kill the bacteria.
For example, efflux pumps found in Gram-negative bacteria actively eliminate chemicals, such as antibiotics, that pass through porins on the outer membrane. These efflux pumps can confer multi-drug resistance, making Gram-negative bacteria more resistant to chemical biocides compared to Gram-positive bacteria.