Which of the following explains the increase of the reaction rate by catalyst?

Options

A. Catalyst decreases the rate of backward reaction so that the rate of forward reaction increases
B. Catalyst provides extra energy to reacting molecules so that they may reduce effective collisions
C. Catalyst provides an alternative path of lower activation energy to the reactants.
D. Catalyst increases the number of collisions between the reacting molecules.

Answer

To solve the question regarding the explanation of how a catalyst increases the reaction rate, we will analyze each option provided and determine which one correctly describes the role of a catalyst.

### Step-by-Step Solution:

1. **Understanding the Role of a Catalyst**:
- A catalyst is a substance that increases the rate of a chemical reaction without being consumed in the process. It achieves this by providing an alternative reaction pathway with a lower activation energy.

2. **Analyzing Each Option**:
- **Option 1**: "The catalyst decreases the rate of backward reaction so that the rate of forward reaction increases."
- This statement is incorrect. A catalyst does not affect the rate of the backward reaction; it accelerates both the forward and backward reactions equally.

- **Option 2**: "Catalyst provides extra energy to reacting molecules so that they may reduce effective collisions."
- This statement is also incorrect. Catalysts do not provide extra energy; rather, they lower the activation energy required for the reaction to occur. Additionally, catalysts do not reduce effective collisions; they facilitate the reaction without changing the collision frequency.

- **Option 3**: "Catalyst provides an alternative path of lower activation energy to the reactants."
- This statement is correct. Catalysts lower the activation energy barrier, allowing the reaction to proceed more easily and quickly. This is the primary way in which catalysts increase reaction rates.

- **Option 4**: "Catalyst increases the number of collisions between the reacting molecules."
- This statement is incorrect. While catalysts may influence the reaction environment, they do not inherently increase the number of collisions between molecules.

3. **Conclusion**:
- Based on the analysis, **Option 3** is the correct explanation of how a catalyst increases the reaction rate. It provides an alternative pathway with lower activation energy, facilitating the reaction.

### Final Answer:
The correct explanation for the increase of the reaction rate by a catalyst is **Option 3: Catalyst provides an alternative path of lower activation energy to the reactants.**