The substance which retards the rate of a reaction is called

Options

A. autocatalyst
B. negative catalyst
C. positive catalyst
D. catalytic poison

Explanation

To solve the question "The substance which retards the rate of a reaction is called," we can follow these steps:

### Step-by-Step Solution:

1. **Understanding the Question**:
- The question is asking for a specific term that describes a substance that slows down a chemical reaction.

2. **Identifying Types of Catalysts**:
- There are different types of catalysts in chemical reactions: positive catalysts, negative catalysts, and autocatalysts.
- Positive catalysts increase the rate of reaction by lowering the activation energy.
- Autocatalysts are products of the reaction that also act as catalysts to speed up the reaction.

3. **Defining Negative Catalyst**:
- A negative catalyst, also known as an inhibitor, is a substance that increases the activation energy barrier for a reaction, thereby slowing down the rate of the reaction.

4. **Conclusion**:
- Based on the definitions, the substance that retards the rate of a reaction is called a **negative catalyst**.

### Final Answer:
The substance which retards the rate of a reaction is called a **negative catalyst**.

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