We can exclude Argon (Ar) and Neon (Ne) they are both very stable. Chlorine (Cl) is reactive but not as much as Fluorine (F). So my answer would be A.
what's the question?
the answer is: trichonympha lives in the gut of termites and digests cellulose eaten by the termite.
this is an example of a symbiotic association of a protozoan with its mode of association.
hope i
-lavira: )