Assign oxidation states to each atom in each element, ion, or compound. Ag, Ca²⁺, BaO, H₂S, NO₃^-, CrO₄^2-

Oxidation states, or oxidation numbers, are a way to keep track of electrons in chemical compounds. They indicate the degree of oxidation of an atom in a substance, helping to determine how electrons are transferred in redox reactions. The oxidation state of an atom can be positive, negative, or zero, depending on its electron gain or loss relative to its elemental form.

There are specific rules for assigning oxidation states, such as: the oxidation state of an element in its standard state is zero; for monoatomic ions, the oxidation state equals the charge; oxygen typically has an oxidation state of -2, and hydrogen is usually +1. These rules provide a systematic approach to determine the oxidation states in various compounds and ions.

Different elements have common oxidation states that are frequently encountered in compounds. For example, alkali metals (like sodium) typically have an oxidation state of +1, while alkaline earth metals (like calcium) usually have +2. Transition metals can have multiple oxidation states, which can complicate their assignment in compounds, making familiarity with these common states essential for accurate analysis.