The change in the oxidation state of iron in the reaction represented by the equation:  $2FeCl_{3} + H_{2}S \to 2FeCl_{2} + 2HCl + S$  is

Step 1: Analyze the question We need to find the oxidation state of iron on both sides of the equation and see how it changes.

Step 2: Concept In a compound, the oxidation states of all atoms add up to the overall charge, which is zero for a neutral compound. Chlorine in metal chlorides is -1.

Step 3: Solution

• In FeCl₃: Fe + 3(-1) = 0, so Fe = +3
• In FeCl₂: Fe + 2(-1) = 0, so Fe = +2

So iron goes from +3 to +2. This is reduction, because the oxidation state decreases. Iron(III) gains one electron:

Fe³⁺ + e⁻ → Fe²⁺

Meanwhile, sulfur in H₂S (-2) goes to elemental S (0), so it is oxidized. H₂S is the reducing agent, and FeCl₃ is the oxidizing agent.

Step 4: Answer The change is +3 to +2, which is option C.

Tip: Remember "OIL RIG": Oxidation Is Loss of electrons, Reduction Is Gain. When an oxidation number goes down (+3 → +2), the species has gained electrons and been reduced. Also, the question asks for the change in the order "from → to," so read the options carefully. Option A (+2 to +3) is the reverse and is a common trap.