The reaction represented by the equation: Ni$^{2+}$$(_{aq}$)  + Fe$(_s$) →  Ni$(_s$)  +  Fe$^{2+}$$(_{aq}$) is a redox reaction because

Step 1: Analyze the question We need to identify what happens to Ni²⁺ and Fe, and which role each plays (oxidizing or reducing agent).

Step 2: Concept

• Oxidation = loss of electrons (oxidation number increases).
• Reduction = gain of electrons (oxidation number decreases).
• A reducing agent is oxidized itself, because it donates electrons.
• An oxidizing agent is reduced itself, because it accepts electrons.
• Memory aid: OIL RIG (Oxidation Is Loss, Reduction Is Gain).

Step 3: Solution

Split into half-equations:

• Ni²⁺(aq) + 2e⁻ → Ni(s) Oxidation number of Ni goes from +2 to 0. Ni²⁺ gains electrons, so it is reduced. This makes Ni²⁺ the oxidizing agent.

• Fe(s) → Fe²⁺(aq) + 2e⁻ Oxidation number of Fe goes from 0 to +2. Fe loses electrons, so it is oxidized. This makes Fe the reducing agent.

Both oxidation and reduction occur at the same time, which is why this is a redox reaction.

Step 4: Check the options

• A: Ni²⁺ oxidized, Fe oxidizing agent. Wrong on both counts.
• B: Ni²⁺ oxidized. Wrong, since it gains electrons.
• C: Ni²⁺ reduced is correct, but Fe as an oxidizing agent is wrong.
• D: Ni²⁺ reduced and Fe a reducing agent. Correct.

Tip: The species that is oxidized is always the reducing agent, and the species that is reduced is always the oxidizing agent. Find which one loses electrons (OIL RIG) and the rest follows. Also, a metal going to its ion (like Fe → Fe²⁺) is always oxidation.