Neutral atom of Ne has 10 electrons. Similarly, Mg\(^{2+}\) has 12 protons(atomic number) and 10 electrons because Mg\(^{2+}\) will donate or give out 2 electrons from the 12 and become reduced to 10 electrons. On the other hand, O\(^{2+}\), Ca\(^{2+}\), and K\(^+\) all have 6, 18 and 18 electrons respectively.