Assertion (A) : For complex reaction, order of reaction is given by the slowest step.
Reason (R) : Order of reaction is not applicable for the complex reaction.
Assertion (A) : For complex reaction, order of reaction is given by the slowest step.
Reason (R) : Order of reaction is not applicable for the complex reaction.
Show Hint
- Both Assertion (A) and Reason (R) are true and Reason (R) is the correct explanation of Assertion (A).
- Both Assertion (A) and Reason (R) are true, but Reason (R) is not the correct explanation of Assertion (A).
- Assertion (A) is true, but Reason (R) is false.
- Assertion (A) is false, but Reason (R) is true.
The Correct Option is C
Solution and Explanation
The order of a reaction is the sum of the powers of the concentration terms in the experimentally found rate law. A complex reaction goes through two or more elementary steps.
Step 2: Check Assertion (A).
In a complex reaction the slowest step controls the overall rate. So the rate law is written from the slowest step (the rate determining step).
The order of the overall reaction is therefore the order found from this slowest step. So (A) is TRUE.
Example: for \( \mathrm{2NO_2 + F_2 \rightarrow 2NO_2F} \), the slow step is \( \mathrm{NO_2 + F_2 \rightarrow NO_2F + F} \), so rate = \( k[\mathrm{NO_2}][\mathrm{F_2}] \) and the order is 2.
Step 3: Check Reason (R).
Order is an experimental quantity. It can be defined for any reaction, simple or complex, and it may even be zero, fractional or negative for a complex reaction.
It is molecularity that is not applicable (not defined) for a complex reaction, because molecularity belongs to a single elementary step.
So the statement that order is not applicable for a complex reaction is FALSE.
Step 4: Compare the options.
Option (1) and (2) need R to be true, but R is false, so both are wrong.
Option (4) says A is false, but A is true, so it is wrong.
Option (3) says A is true and R is false, which matches our findings.
Final Answer:
A is true and R is false, which is option (3). \[ \boxed{\text{Option (3)}} \]
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