Choose the correct statement about O_3 chemistry in stratosphere. A. Third molecule such as N_2 or H_2 O carry away the heat generated during ozone

Question

Choose the correct statement about O_3 chemistry in stratosphere.
A. Third molecule such as N_2 or H_2 O carry away the heat generated during ozone formation.
B. Conversion of inactive to active chlorine occurs at the surface of particles formed by a solution of water.
C. Process of denitrification in lower stratosphere enhances/helps in ozone destruction.
D. OH/H_2 O is a catalytic cycle for ozone destruction.
E. [O_3 ]_ss/[O_2 ]_ss ratio is directly proportional to air density through third body molecules [M], not involved in ozone formation/destruction process.
Choose the most appropriate answer from the options given below:

A, B, C and D only

A, B, C and E only

A, B and C only

A, C and D only

Solution

Correct option is C

Introduction

Stratospheric ozone chemistry involves a dynamic balance of formation and catalytic destruction cycles, mediated by third-body molecules, halogen radicals, and heterogeneous reactions on particle surfaces.

Understanding these mechanisms is central to explaining ozone-layer depletion.

Information Booster

A. A third molecule (N₂ or H₂O) carries away the heat generated during ozone formation. Correct. In the recombination step O + O₂ + M → O₃ + M, a third body M (commonly N₂ or O₂) is essential to absorb the excess energy released, stabilising the newly formed ozone molecule; without M, the energised O₃ would immediately dissociate.
B. Conversion of inactive to active chlorine occurs on the surface of particles formed from a solution of water. Correct. On polar stratospheric cloud (PSC) particles ice and supercooled ternary/water solutions heterogeneous reactions convert reservoir species (ClONO₂, HCl) into photolytically active chlorine (Cl₂), which then releases ozone-destroying Cl radicals in spring sunlight.
C. Denitrification in the lower stratosphere enhances ozone destruction. Correct. Denitrification removes nitrogen oxides (as HNO₃ sedimenting in PSC particles), preventing NOₓ from sequestering active chlorine into inert ClONO₂; with less NOₓ available, active chlorine persists longer, intensifying ozone loss.

Additional knowledge

D. OH/H₂O is a catalytic cycle for ozone destruction — Treated as incorrect here. The genuine hydrogen catalytic cycle is the HOₓ cycle (OH/HO₂), not "OH/H₂O." Water vapour is the source of HOₓ radicals but is not itself the catalytic pair; the cycle operates through OH and HO₂ interconversion, so the statement as written mislabels the catalyst.
· E. [O₃]ss/[O₂]ss ratio is directly proportional to air density through third-body [M] not involved in the process — Incorrect. The third-body molecule [M] is directly involved in the ozone-formation step (O + O₂ + M → O₃ + M); describing [M] as "not involved in ozone formation/destruction" contradicts its essential stabilising role, and the proportionality claim is mis-stated.