Respuesta :
1. Protons (p) and neutrons(n): Be 4p and 5n, Mg 12p and 12n, Ca 20p and 20n, Sr 38p and 50n, Ba 56p and 81n and Pa 88p and 138n. They react with hydrogen to form metallic hydrides, with oxygen to form oxides and react with halogens to form metallic halides. All elements in Group 2 have two electrons in their valence shells.