Final answer:
Alkaline earth metals in Group 2 of the periodic table always have an oxidation number of +2. This is due to their two valence electrons in the outer shell which they readily donate, becoming divalent cations in chemical reactions.
Step-by-step explanation:
The alkaline earth metals found in Group 2 of the periodic table always have an oxidation number of +2. These elements, which include beryllium (Be), magnesium (Mg), calcium (Ca), strontium (Sr), barium (Ba), and radium (Ra), have two electrons in their outer s-electron shell. In chemical reactions, alkaline earth metals lose these two valence electrons to form cations with a +2 charge, reflecting their oxidation number of +2. This property is due to the fact that these metals are divalent, which means they are ready to donate both valence electrons during reactions, becoming highly reactive, especially when compared to alkali metals in Group 1 that have an oxidation state of +1.