Consider the three gas-phase elementary reactions listed below, all of which occur in the lower atmosphere.
Reaction (I) NO₂(g) + Cl(g) → NO₂Cl(g)
Reaction (II) 2 NO(g) + O₂(g) → 2 NO₂(g)
Reaction (III) O(g) + O₂(g) + M → O₃(g) + M (M represents an inert collision partner that is not consumed.)
(a) For each elementary reaction, classify its molecularity and state the numerical value of that molecularity.
(b) For Reaction (II), write the rate law expression and state the overall reaction order.
(c) Describe, with specific reference to Reactions (I)–(III), the difference between molecularity and overall reaction order.
(d) Explain why elementary reactions such as Reaction (III) are observed far less frequently than elementary reactions such as Reaction (I).