Group 16 Ozone

The reactivity and instability of ozone are linked to its thermodynamics. The formation of ozone from oxygen, 3O_2 → 2O_3, is endothermic with a positive enthalpy change, meaning ozone stores extra energy compared with ordinary dioxygen. Because of this stored energy, ozone readily decomposes back to oxygen, releasing energy and liberating a reactive nascent oxygen atom that makes ozone a powerful oxidising agent. The option that its formation is exothermic is incorrect, since the reverse holds. The option that it is a noble gas is false, as ozone is a reactive form of oxygen. The option that it has no oxygen atoms is absurd, since ozone is triatomic oxygen, O_3. The endothermic formation and consequent oxidising power of ozone are key NCERT facts for Group 16. A common JEE pitfall is to ignore the role of ozone, yet it is exactly this factor that distinguishes the correct answer from the tempting alternatives. It is worth emphasising that this is not a special case but a representative example of how group 16 ozone operates throughout p-block elements. Plausibility check: the positive enthalpy of formation directly explains both ozone's tendency to decompose and its strong oxidising action through released nascent oxygen, confirming the answer.