An atom has 20 neutrons and 19 protons in its nucleus. How many
electrons are in its outer (valence) electron shell? How many
shells does it have? What is its atomic mass in g/mol? What is the
element?
1, 3, 39, K
1, 4, 19, Mg
2, 4, 19, Mg
2, 4, 39, K
1, 4, 39, K