Which of the following describes the electron sharing between hydrogen and fluorine?
a. hydrogen shares one electrons, while fluorine shares seven electrons.
b. hydrogen shares seven electrons, while fluorine shares one electrons.
c. hydrogen and fluorine share one electron with each other.
d. hydrogen and fluorine share seven electrons with each other.

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We know both the elements involved in bonding are non-metals and the primary type of bonds involved in non-metals are covalent bonds. Covalent bonds are formed when two atoms share one or more electrons; thus we know that whatever the number of electrons shared, it has to be equal for both. We can eliminate choices A and B.
Next, we understand that it is easier for one atom to be shared among the two, rather than the 7. First, because Hydrogen needs only 1 electron to be stable and would require energy to compensate the remaining 6. Second, electrons are attracted towards the nucleus so it is inefficient to try and share 7 electrons when 1 provides the same amount of stability to Fluorine.
Therefore, the answer is C.