Question: how many valence electrons are in an atom of magnesium (atomic number 12)?
Answer: Magnesium is element 12 and belongs to Group 2 of the Periodic Table. An element in Group 2 has two valence electrons. Also, the electron configuration of Mg is 1s² 2s²2p⁶ 3s² or [Ne]3s². Since the 3s² electrons are the outermost electrons, magnesium has two valence electrons.