Which term correctly classifies O2 and O3 as 'allotropic forms'?

• A. Isotopes
• B. Allotropes
• C. Compounds
• D. Ions

Answer: (B)

Allotropy is when an element exists in more than one structural form in the same state. Oxygen shows this with O2 and O3, two different ways the same element can bond and arrange its atoms. O2 is a diatomic molecule with two oxygens linked mainly by a double bond, while O3 (ozone) has a bent arrangement with a resonance that spreads bonding across three oxygens. That difference in bonding and structure makes them distinct forms of the same element, hence allotropes.

Isotopes would be variants of the nucleus with different numbers of neutrons, leading to different atomic masses, not different molecular structures like these. Compounds are substances made from two or more elements chemically bonded together, while oxygen molecules are pure elemental forms. Ions are charged species; the standard forms of O2 and O3 are neutral molecules, though ionized versions exist in other contexts.

So, O2 and O3 are different allotropic forms of oxygen.