Which of the following reactions is given by ozone (O_3) ?

The correct answer is Option (1) → PbS(s) + 4O₃(g) → PbSO₄(s) + 4O₂(g)

Ozone readily gives up nascent oxygen (\( \ce{O3} \) → \( \ce{O2} \) + O), so it is a powerful oxidising agent. It oxidises lead sulphide (S at −2) to lead sulphate (S at +6):

    \( \ce{PbS(s) + 4O3(g) -> PbSO4(s) + 4O2(g)} \)

Every reaction of ozone must therefore show the other reactant being oxidised.

Why the other options are incorrect

• Option (2) — Incorrect. It shows iodine being reduced to iodide ions. Ozone does the reverse: it oxidises iodide to iodine, \( \ce{2I- + H2O + O3 -> 2OH- + I2 + O2} \).

• Option (3) — Incorrect. It shows \( \ce{Fe^{3+}} \) being reduced to \( \ce{Fe^{2+}} \); an oxidising agent cannot reduce another species.

• Option (4) — Incorrect. It shows \( \ce{Sn^{4+}} \) being reduced to \( \ce{Sn^{2+}} \), which again is the opposite of what ozone does.

Note: This question is from the pre-rationalised NCERT book (2022-23). The topic is not there in the latest NCERT book (2026-27), and it is also out of the CUET 2026 syllabus.

NCERT (Pre-rationalised edition, 2022-23):
Properties – “… Due to the ease with which it liberates atoms of nascent oxygen (O₃ → O₂ + O), it acts as a powerful oxidising agent. For e.g., it oxidises lead sulphide to lead sulphate and iodide ions to iodine.
PbS(s) + 4O₃(g) → PbSO₄(s) + 4O₂(g)
2I⁻(aq) + H₂O(l) + O₃(g) → 2OH⁻(aq) + I₂(s) + O₂(g)”