Question

Which of the following is an elementary reaction ?

• A. \(\text{O}_{3(g)}\rightarrow \text{O}_{2(g)}+\text{O}_{(g)}\)
• B. \(2\text{NO}_2\text{Cl}_{(g)}\rightarrow 2\text{NO}_{2(g)}+\text{Cl}_{2(g)}\)
• C. \(2\text{NO}_{2(g)}+\text{F}_{2(g)}\rightarrow 2\text{NO}_2\text{F}_{(g)}\)
• D. \(2\text{NO}_{(g)}+\text{Cl}_{2(g)}\rightarrow 2\text{NOCl}_{(g)}\)

Hint:

An elementary reaction occurs in a single step; its molecularity is small and equals the number of reacting species.

Answer 1

The Correct Option is A

Step 1: Understanding the Concept:
An elementary reaction occurs in one step, with the collision of at most three species. Complex reactions have several steps.

Step 2: Check Option (A):
\(\text{O}_3 \rightarrow \text{O}_2 + \text{O}\) involves a single molecule breaking into two pieces in one step. This is a unimolecular elementary reaction.

Step 3: Check the Other Options:
\(2\text{NO}_2\text{Cl} \rightarrow 2\text{NO}_2 + \text{Cl}_2\) is known to occur in two steps (slow step produces \(\text{NO}_2 + \text{Cl}\)), so it is complex.
\(2\text{NO}_2 + \text{F}_2 \rightarrow 2\text{NO}_2\text{F}\) is known to occur in two steps through \(\text{NO}_2\text{F}\) and F atoms.
\(2\text{NO} + \text{Cl}_2 \rightarrow 2\text{NOCl}\) has three reacting molecules, and its mechanism involves an intermediate \(\text{NOCl}_2\), so it is not a single step.

Step 4: Conclusion:
The decomposition of ozone as written is the elementary step.

Final Answer:
Option (A) is a single-step unimolecular process. \[ \boxed{\text{(A) } \text{O}_{3(g)}\rightarrow \text{O}_{2(g)}+\text{O}_{(g)}} \]