Concept:The reducing power of halogen atoms depends on their ease of losing an electron.
Explanation:A reducing agent donates electrons and is itself oxidised.
The more easily an atom loses its outermost electron, the stronger its reducing action.
Down the halogen group, atomic size increases from fluorine to iodine.
Larger atomic size means lower ionisation energy.
Among the given species, iodine has the largest atomic radius and the lowest ionisation energy.
So, an iodine atom loses its outer electron most easily.
Therefore, iodine atom is the most powerful reducing agent.
Answer:D. Iodine atom