Question

Given below is the decomposition of hydrogen peroxide in alkaline medium, which is catalysed by iodide ions: \[ 2H_2O_2 \xrightarrow{I^-, \; \text{alkaline medium}} 2H_2O + O_2 \] The above reaction takes place in two steps:
Step I: \( H_2O_2 + I^- \longrightarrow H_2O + IO^- \) (slow)
Step II: \( H_2O_2 + IO^- \longrightarrow H_2O + I^- + O_2 \)
Molecularity of Step I and Step II is:

• A. Step I – 2, Step II – 2
• B. Step I – 1, Step II – 2
• C. Step I – 2, Step II – 1
• D. Step I – 3, Step II – 1

Hint:

Molecularity counts the actual number of reacting species in a single step — it is always a whole number.

Answer 1

The Correct Option is A

Step 1: Molecularity is the total number of reactant species involved in an elementary step.
Step 2: For Step I: \( H_2O_2 + I^- \)
\[ \text{Number of species} = 2 \quad \Rightarrow \text{Molecularity} = 2 \] Step 3: For Step II: \( H_2O_2 + IO^- \)
\[ \text{Number of species} = 2 \quad \Rightarrow \text{Molecularity} = 2 \] Step 4: So, both steps have a molecularity of 2.