What happens when a sodium atom and a chlorine atom exchange an electron?

Sodium Chloride salt is formed through the formation of an ionic bond.

Explanation:

Sodium atom possess one electron in its outer shell and chlorine possess seven electrons in its outer shell.

When electron exchange occurs between the two then sodium atom gives its electron to chlorine and thus becomes positive sodium ion and by accepting that electron from sodium, the chlorine atom becomes the negative chloride ion. Which results in the completion of outer shells of both the atoms.

Therefore through this interaction of oppositely charged ions an ionic lattice is formed which is called as the sodium chloride salt.

i think the answer is b.