a) The most chance of being an insomniac is not the overworked executive or the student overwhelmed by the studies but the bored housewife who feels unfulfilled.
After the most chance of being an insomniac has to come something that makes sense.
For instance
The main problem of being a smart person is not the student or the professor ... This does not make any sense.
b) The highest degree of insomnia is not experienced by the overworked executive nor by the student overwhelmed by studies but by the bored housewife who feels unfulfilled.
This seems to be the better among the answer choices although I miss rather after but to use the correlative
not by X but rather by Y.
c) Most insomniacs are not overworked executives or students overwhelmed by studies, yet they are bored housewives who feels unfulfilled.
This construction changes the meaning of the sentence. The second part housewives who feels has a Suject-verb agreement error. Perhaps this is a typo.
d) The greater degree of insomniacs are bored housewives who feel unfulfilled and not overworked executives nor are they students overwhelmed by studies.
The greater degree of insomniacs ---> I think this is not correct construction
e) Insomniacs are, for the most part, bored housewives who feel unfulfilled, not overworked executives or students overwhelmed by their studies.
I believe that we need either a coordinator or subordinator to join the phrase
not overworked executives or students overwhelmed by their studiesInsomniacs are bored housewives who feel unfulfilled, not overworked executives or students overwhelmed by their studies.