In reducing conditions, what is the common ion formed from ferrous iron?

In reducing conditions, ferrous iron, which is represented as Fe²⁺, is indeed the common species found. Under these conditions, there is a tendency for iron to stay in its +2 oxidation state rather than being oxidized to the +3 state (Fe³⁺) or further beyond. When conditions are reducing, there is an abundance of electrons that can stabilize the lower oxidation states of metals, such as Fe²⁺.

Fe²⁺ is commonly found in various environments such as in biological systems and certain geological settings where reducing conditions prevail. This ion is crucial for biological processes, including the transport of oxygen in hemoglobin, and serves as a fundamental component in many chemical reactions within both inorganic and biochemical contexts.

The other oxidation states of iron, such as Fe³⁺ and Fe⁴⁺, would require oxidizing conditions to be present, which is contrary to the scenario described in the question. In the case of elemental iron (Fe), while it is a product of reduction, the specific inquiry about the common ion in solution points directly to Fe²⁺. Thus, under reducing conditions, Fe²⁺ is the prevalent species formed from ferrous iron.