Assertion : Molecularity greater than three is not observed.
Reason : The overall molecularity of complex reaction is equal to molecularity of the slowest step.

Options

A. If both assertion and reason are true and reason is the correct explanation of assertion.
B. If both assertion and reason are true but reason is not the correct explanation of assertion.
C. If assertion is true but reason is false.
D. If both assertion and reason are false.

Explanation

To analyze the given assertion and reason, we can break down the solution into clear steps:

### Step 1: Understand Molecularity
Molecularity is defined as the number of reactant species (molecules, atoms, or ions) that collide simultaneously to bring about a chemical reaction.

**Hint:** Recall that molecularity can be unimolecular (1), bimolecular (2), or trimolecular (3).

### Step 2: Analyze the Assertion
The assertion states that "Molecularity greater than three is not observed." This is generally true because reactions involving four or more molecules colliding simultaneously are exceedingly rare due to the improbability of such collisions occurring at the same time.

**Hint:** Consider the physical limitations of molecular collisions in a given volume.

### Step 3: Analyze the Reason
The reason provided states that "The overall molecularity of a complex reaction is equal to the molecularity of the slowest step." This statement is incorrect because the overall molecularity of a complex reaction cannot be defined in terms of the slowest step alone. Instead, the rate of the reaction is determined by the slowest step, but molecularity is defined for individual elementary steps.

**Hint:** Remember that the rate-determining step influences the rate of the reaction, but does not define the overall molecularity of the entire reaction mechanism.

### Step 4: Conclusion
From the analysis, we conclude that the assertion is true, as molecularity greater than three is not typically observed. However, the reason is false because it misrepresents the concept of molecularity in complex reactions.

**Final Answer:** The assertion is true, but the reason is incorrect.