Based on the electron configurations and orbital spin diagrams for the neutral atom and the ion of the element having atomic number 12

Question

explain the valence number of electrons in the element responsible for the ion's charge 

Answer 1

The element in question is magnesium (Mg) with atomic number 12.  In the neutral atom it has an electron configuration of 1s2 2s2 2p6 3s2 and the orbital diagram is ↑↓  ↑↓  ↑↓↑↓↑↓   ↑↓.

 

The valence electron are those in the 3s subshell and these are lost to create an ion of Mg2+ that is isoelectronic with neon.