Answer:
A covalent bond forms when the difference between the electronegativities of two atoms is too small for an electron transfer to occur to form ions. Shared electrons located in the space between the two nuclei are called bonding electrons. The bonded pair is the “glue” that holds the atoms together in molecular units.
Symbiosis in lichens is the mutually helpful symbiotic relationship of greenalgae and/or blue-green algae(cyanobacteria) living among filaments of a fungus, forming lichen. The algaeor cyanobacteria benefit their fungalpartner by producing organic carbon compounds through photosynthesis
