Assertion (A): The molecularity of the given reaction is 2 $2HI \longrightarrow H_2 + I_2$ Reason (R): Two molecules of the reactants are involved in simultaneous collision between them.
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Molecularity is determined by counting the stoichiometric coefficients of reactants in a single-step elementary reaction.
Both Assertion (A) and Reason (R) are true and Reason (R) is the correct explanation of the Assertion (A).
Both Assertion (A) and Reason (R) are true, but Reason (R) is not the correct explanation of the Assertion (A).
Assertion (A) is true, but Reason (R) is false.
Assertion (A) is false, but Reason (R) is true.
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The Correct Option isA
Solution and Explanation
Step 1: Definition of molecularity. Molecularity is the number of reacting species that participate in a single elementary reaction step. These species must collide simultaneously for the reaction to occur. Step 2: Analyse the given reaction. The reaction $2HI \rightarrow H_2 + I_2$ is treated as an elementary step. It involves two $HI$ molecules that must collide together. Therefore its molecularity is 2 (bimolecular). Assertion (A) is TRUE. Step 3: Evaluate Reason (R). Reason (R) states that two molecules of reactant are involved in simultaneous collision. This is precisely the definition of a bimolecular reaction. Reason (R) is also TRUE. Step 4: Explanatory link. The molecularity is 2 because two HI molecules must collide simultaneously. R directly explains why A is true. Both A and R are correct and R is the correct explanation. \[ \boxed{(A)} \]