Question

Assertion (A): The molecularity of the given reaction is 2. \[ 2\text{HI} \rightarrow \text{H}_2 + \text{I}_2 \] Reason (R): Two molecules of the reactants are involved in simultaneous collision between them. Choose the correct option:

• A. Both Assertion (A) and Reason (R) are true and Reason (R) is the correct explanation of the Assertion (A).
• B. Both Assertion (A) and Reason (R) are true, but Reason (R) is not the correct explanation of the Assertion (A).
• C. Assertion (A) is true, but Reason (R) is false.
• D. Assertion (A) is false, but Reason (R) is true.

Hint:

Molecularity = number of molecules colliding in an elementary step. 1 → Unimolecular 2 → Bimolecular 3 → Termolecular (rare)

Answer 1

The Correct Option is A

Concept: Molecularity is defined as the number of reacting species that collide simultaneously in an elementary reaction step. It is always a whole number.
Step 1: Check Assertion (A). Given reaction: \[ 2\text{HI} \rightarrow \text{H}_2 + \text{I}_2 \] Two HI molecules are involved in the reaction step. Hence, molecularity = 2 (bimolecular reaction). Assertion is true.
Step 2: Check Reason (R). Molecularity depends on the number of molecules colliding simultaneously. Here, two molecules of HI collide. Reason is true.
Step 3: Check if Reason explains Assertion. Since molecularity is defined based on simultaneous collisions, the reason correctly explains why molecularity is 2.