Assertion (A ): Molecularity of a reaction cannot be more than three
Reason (R ): Probability of simultaneous collision between more than three particles is very less.

Options

A. Both (A) and (R) are true (R) is the correct explanation to (A)
B. Both (A) and (R) are true but (R) is not the correct explanation to (A)
C. (A) is true but (R) is false
D. Both (A) and (R) are false

Explanation

To solve the question regarding the assertion and reason, we will analyze both statements step by step.

### Step 1: Understanding Molecularity
Molecularity is defined as the number of reactant molecules involved in an elementary reaction. It is determined by the sum of the stoichiometric coefficients of the reactants in that reaction.

**Hint:** Remember that molecularity refers to the number of reactant species in a single step reaction.

### Step 2: Analyzing the Assertion (A)
The assertion states that the molecularity of a reaction cannot be more than three. This is generally true because:
- Elementary reactions can be unimolecular (1 reactant), bimolecular (2 reactants), or trimolecular (3 reactants).
- Reactions involving more than three reactants simultaneously are extremely rare due to the complexity of simultaneous collisions.

**Hint:** Think about how many molecules can realistically collide at the same time to form products.

### Step 3: Analyzing the Reason (R)
The reason provided states that the probability of simultaneous collisions between more than three particles is very low. This is also true because:
- As the number of particles increases, the likelihood of all of them colliding at the same time decreases significantly.
- Effective collisions are essential for reactions to occur, and the probability of effective collisions decreases with more particles.

**Hint:** Consider how crowded conditions affect the likelihood of collisions among particles.

### Step 4: Conclusion
Both the assertion and the reason are correct:
- The assertion (A) that the molecularity of a reaction cannot be more than three is true.
- The reason (R) that the probability of simultaneous collisions between more than three particles is very low is also true and explains why the molecularity is limited.

Thus, both A and R are correct, and R provides the correct explanation for A.

**Final Answer:** Both A and R are true, and R is the correct explanation of A.