Http://i66.tinypic.com/2m7uul4.jpg - Question 10 why is the answer (d)..?

A. False
There is no reaction between aqueous Fe²⁺ and acidified I⁻. This is because both of Fe²⁺ and I⁻ are reducing agent and FeI₂ is soluble in water.

B. False
Precipitation reaction occurs, but the reaction is not redox because there is no change in oxidation number.
Fe²⁺(aq) + 2OH⁻(aq) → Fe(OH)₂(s)

C. False
Precipitation reaction occurs, but the reaction is not redox because there is no change in oxidation number.
Ba²⁺(aq) + SO₄²⁻(aq) → BaSO₄(s)

D. True
Redox reaction occurs because aqueous Fe²⁺ is a reducing agent while O₂ is an oxidizing agent. The two half equations are :
Fe²⁺(aq) → Fe³⁺(aq) + e⁻
O₂(g) + 2H₂O(l) + 4e⁻ → 4OH⁻(aq)

...... The answer is : D. oxygen

No problem shown.