What is the number of valence electrons in :(a) sodium ion, Na⁺(b) oxide ion, O^2–

(a) Atomic number of sodium atom = 11

In Na⁺ ion, there are only 10 electrons. The electronic configuration is 2 , 8. Therefore, the number of valence electrons in sodium ion is 8.

(b) Atomic number of oxygen atom = 8

In O^2- ion, there will be 10 electrons, as it has gained two electrons. The electronic configuration is 2, 8. Therefore, the number of valence electrons in O^2- is 8.