The covalent bond which links the cell walls of gram-positive bacteria containing two modified sugars – N – acetylmuramic acid (NAM) and N-acetyl glucosamine (NAG) is

The correct option is 1,4-glycosidic bond.

Step-by-step Explanation:
1. Composition of the Bacterial Cell Wall: The cell wall of gram-positive bacteria is characterized by a thick, protective layer of peptidoglycan (also known as murein). Peptidoglycan is a polymer consisting of sugars and amino acids.
2. The Sugar Backbone: The glycan portion of peptidoglycan is composed of alternating units of two modified amino sugars:
- N-acetylglucosamine (NAG)
- N-acetylmuramic acid (NAM)
3. Formation of the Glycosidic Linkage: These alternating NAG and NAM monomeric units are joined together to form long chains. The covalent bond is formed via a condensation reaction between the anomeric carbon-1 (C-1) of one sugar monomer and the hydroxyl group on carbon-4 (C-4) of the adjacent sugar monomer.
4. Conclusion: Because the connection occurs specifically between the carbon-1 and carbon-4 positions of the sugars in a beta-orientation, the linkage is a β-1,4-glycosidic bond (commonly referred to as a 1,4-glycosidic bond).