The atoms in the answer choices have at least 2 electron shells each.Which atom would tend to lose 1 valence electron to another atom in order to become stable?

- The outermost shell of an atom consists (except in the case of hydrogen and helium) of 8 valence electrons. Therefore, every atom tends to fullfill its outermost shell by accepting or giving away electrons, according to how many it currently has in its outermost shell.

This means that atoms that have more than 4 valence electrons (5,6,7) tend to gain electrons from other atoms, in order to reach 8 in their outermost shell, while atoms that have less than 4 valence electrons (1,2,3) tend to lose electrons in order to empty their outermost shell (so their last-but-one outermost shell will become the last one, and will be completed with 8 electrons).

In this case, we see that the atom of sodium, Na, has only 1 valence electron in its outermost shell: therefore, it will tend to lose this electron in order to have its outermost shell completed.