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MHTCET 19 Apr 2026 Shift 1 Paper

Question : 77 of 150

Marks: +1, -0

Which of the following is an elementary reaction?

$\mathrm{O}_{3(g)} \rightarrow \mathrm{O}_{2(g)}+\mathrm{O}_{(g)}$
$2 \mathrm{NO}_{2} \mathrm{Cl}{ }_{(g)} \rightarrow 2 \mathrm{NO}_{2(g)}+\mathrm{Cl}_{2(g)}$
$2 \mathrm{NO}_{2(g)}+\mathrm{F}_{2(g)} \rightarrow 2 \mathrm{NO}_{2} \mathrm{~F}_{(g)}$
$2 \mathrm{NO}_{(g)}+\mathrm{Cl}_{2(g)} \rightarrow 2 \mathrm{NOCl}{ }_{(g)}$

Solution:

Concept:

An elementary reaction is a reaction that occurs in a single step, with no intermediate species formed.

Explanation:

In option A, one molecule of ozone decomposes directly in one step:

\mathrm{O}_{3(g)} \rightarrow \mathrm{O}_{2(g)}+\mathrm{O}_{(g)}

This is a unimolecular elementary reaction because only one molecule participates in the rate-determining step.

The other given reactions have balanced equations that represent overall reactions, not single-step elementary processes.

They are complex reactions involving multiple elementary steps.

Therefore, only option A is an elementary reaction.

Answer:

Option A

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