(Correct Answer receives brainliest)

                  Option-A ( Fe²⁺ ₍aq₎ + 2 e⁻   →   Fe ₍s₎ ) is the correct answer.

Explanation:

                    In inorganic chemistry oxidation and reduction reactions are defined as;

                  Oxidation Reaction:

                                                   Those reactions (mainly half reactions) in which the atom loses electrons are called as oxidation reactions. In given example the Magnesium is oxidized as it loses two electrons to for Mg²⁺ i.e.

                                   Mg ₍s₎   →   Mg²⁺ ₍aq₎  +  2 e⁻

                  Reduction Reaction:

                                                   Those reactions (mainly half reactions) in which the atom gains electrons are called as reduction reactions. In given example the Iron Ion (Fe²⁺) is reduced as it gains two electrons to form Fe i.e.

                                   Fe²⁺ ₍aq₎ + 2 e⁻   →   Fe ₍s₎