Answer: A) 2+
Explanation: Magnesium is an element with atomic number 12 and thus contain 12 electrons. It is a s block element as the last electron enters the s orbital. The nearest noble gas is Neon with 10 electrons.
The electrons are filled according to Afbau's rule in order of increasing energies and thus the electronic configuration is:
[tex]Mg:12:1s^22s^22p^63s^2[/tex]
Thus Magnesium loses two valence electrons so as to attain stable configuration and forms a [tex]Mg^{2+}[/tex] ion with noble gas configuration.
[tex]Mg^{2+}:10:1s^22s^22p^6[/tex]
