The element from the options provided that commonly exhibits an oxidation state of +2 is Strontium (Sr). Let's elaborate on this answer. Strontium belongs to the group 2 elements of the periodic table, which are also known as the alkaline earth metals. Elements in this group typically lose two electrons to form ions with a +2 charge in order to achieve a noble gas configuration. This means that Sr2+ is the common ion formed by strontium when it reacts with nonmetals or in other chemical reactions where it is oxidized. Now, let's consider the other options: Rubidium (Rb) - This is an alkali metal that belongs to group 1 of the periodic table. Alkali metals typically have an oxidation state of +1 due to the loss of their single valence electron to form a cation (Rb+). Sodium (Na) - Similar to rubidium, sodium is also an alkali metal and typically loses one electron to form an Na+ion with a+1 oxidation state. Lithium (Li) - Lithium is the lightest metal and the first element in the alkali metals group. Like the other group 1 elements, it exhibits an oxidation state of +1 when it forms a Li+ion. In summary, Sr most commonly exhibits the +2 oxidation state, making option A(Sr) the correct answer to the question.