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MHTCET 11 May 2024 Shift 1 Paper

Question : 58 of 150

Marks: +1, -0

Which of the following is an elementary reaction?

$C_{2} \mathrm{H}_{5} \mathrm{I}_{(\mathrm{g})} \longrightarrow C_{2} \mathrm{H}_{4(\mathrm{~g})}+\mathrm{HI}_{(\mathrm{g})}$
$2 \mathrm{NO}_{2} \mathrm{Cl}_{(\mathrm{g})} \longrightarrow 2 \mathrm{NO}_{2(\mathrm{z})}+\mathrm{Cl}_{2(\mathrm{z})}$
$2 \mathrm{NO}_{2(\mathrm{~g})}+\mathrm{F}_{2(\mathrm{~g})} \longrightarrow 2 \mathrm{NO}_{2} \mathrm{~F}_{(\mathrm{g})}$
$2 \mathrm{NO}_{(\mathrm{g})}+\mathrm{Cl}_{2(\mathrm{~g})} \longrightarrow 2 \mathrm{NaCl}_{(\mathrm{g})}$

Solution:

Concept:

An elementary reaction is a single-step reaction whose rate law can be written directly from its balanced equation.

Explanation:

In an elementary reaction, the number of molecules that collide is equal to its balanced stoichiometric coefficients.

Option A represents a unimolecular decomposition of ethyl iodide occurring in one step:

\mathrm{C_2H_5I_{(g)}} \longrightarrow \mathrm{C_2H_{4(g)}} + \mathrm{HI_{(g)}}

This reaction involves a single reactant molecule breaking down directly, so it is an elementary reaction.

The other options involve multiple reactant molecules and are not given as single-step elementary processes.

Answer:

\mathrm{C_2H_5I_{(g)}} \longrightarrow \mathrm{C_2H_{4(g)}} + \mathrm{HI_{(g)}}

is the elementary reaction. Hence, option A is correct.

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