Answer;
Complete
Valence is the number of electrons an atom must gain or lose in order to complete its outer energy level or have a stable octet in its outer shell.
Explanation;
-Valency is the number of electrons that an atom requires to gain or lose to form a complete configuration or an octet configuration.
-Atoms tend to lose or get electrons in order to achieve the electronic arrangement of atoms of the noble gases. An ion is an atom or group of atoms having an overall electrical charge. Atoms gain electrons to form cations (positively charged atom), while other lose to form anions (negatively charged atoms).
