What is the probability of reaction with molecularity higher than three very rare?

Explanation

To understand why the probability of reactions with molecularity higher than three is very rare, we can break down the explanation into several steps:

### Step-by-Step Solution:

1. **Definition of Molecularity**:
- Molecularity is defined as the number of reactant molecules that collide simultaneously to bring about a chemical reaction. It is an important concept in chemical kinetics.

2. **Examples of Molecularity**:
- For instance, in the reaction where two hydrogen molecules react with one oxygen molecule to form two water molecules, the molecularity is calculated as:
\[ \text{Molecularity} = \text{(number of hydrogen molecules)} + \text{(number of oxygen molecules)} = 2 + 1 = 3 \]

3. **Understanding Effective Collisions**:
- For a reaction to occur, the colliding molecules must have effective collisions. An effective collision is one that has sufficient energy (threshold energy) and the correct orientation.

4. **Challenges with Higher Molecularity**:
- As the molecularity increases beyond three, the likelihood of multiple molecules colliding simultaneously with the correct orientation and energy decreases significantly.
- This is because the probability of three or more molecules colliding at the same time is much lower than that of two molecules colliding.

5. **Conclusion on Reaction Probability**:
- Due to the decreased chances of effective collisions when molecularity exceeds three, reactions with higher molecularity are very rare.
- Thus, reactions with molecularity greater than three are unlikely to occur because they require a very specific set of conditions that are hard to achieve.

### Summary:
The probability of reactions with molecularity higher than three is very rare because the likelihood of effective collisions decreases significantly as the number of colliding molecules increases.

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