Answer: A. Na only
Step-by-step explanation:
An ionic bond is formed when an element completely transfers its valence electron to another element. The element which donates the electron is known as electropositive element and forms a positively charged ion called as cation. The element which accepts the electrons is known as electronegative element and forms a negatively charged ion called as anion.
Electronic configuration of sodium:
![[Na]=1s^22s^22p^63s^1](https://img.qammunity.org/2017/formulas/biology/high-school/4ay35e4bz2yqwwa0773viu0eche9cmuamv.png)
Sodium atom will loose one electron to gain noble gas configuration and form sodium cation with +1 charge.
![[Na^+]=1s^22s^22p^63s^0](https://img.qammunity.org/2017/formulas/biology/high-school/3j0ihiprtqodyku9tzapktjl8sz9eebkie.png)
Electronic configuration of chlorine:
![[Cl]=1s^22s^22p^63s^23p^5](https://img.qammunity.org/2017/formulas/biology/high-school/25e9s1l4sq39a62edz9ahmcow0bmjm5m3p.png)
Chlorine atom will gain one electron to gain noble gas configuration and form chloride ion with -1 charge.
![[Cl^-]=1s^22s^22p^63s^23p^6](https://img.qammunity.org/2017/formulas/biology/high-school/s1g64qvi56xdkzq8l15v9iwz8d95ceacxa.png)