Substances which alter the speed of a chemical reaction without themselves undergoing a permanent change are known as

Options

A. promoters
B. catalysts
C. inhibitors
D. alums

Explanation

To solve the question, we need to identify the correct term for substances that alter the speed of a chemical reaction without undergoing a permanent change themselves. Let's go through the options provided:

1. **Promoter**:
- A promoter is a substance that increases the activity of a catalyst. However, it does not directly alter the speed of a reaction on its own. It enhances the effectiveness of a catalyst but is not the main agent that speeds up the reaction.

2. **Catalyst**:
- A catalyst is defined as a substance that increases the speed of a chemical reaction without undergoing any permanent change itself. This means that after the reaction, the catalyst can be recovered in its original form. This fits the definition given in the question perfectly.

3. **Inhibitor**:
- An inhibitor is often referred to as a negative catalyst because it decreases the rate of a reaction. This is the opposite of what we are looking for in this question.

4. **Alum**:
- Alum is a specific chemical compound (a double sulfate of aluminum) and does not relate to the general concept of altering reaction speeds.

Based on the analysis of the options, the correct answer is:

**Option B: Catalyst**

### Step-by-Step Solution:
1. **Identify the definition**: Understand that we are looking for a substance that alters the speed of a reaction without undergoing a permanent change.
2. **Analyze each option**:
- **Promoter**: Enhances catalytic activity but does not directly speed up reactions.
- **Catalyst**: Increases reaction speed and remains unchanged after the reaction.
- **Inhibitor**: Decreases reaction speed; not applicable here.
- **Alum**: A specific compound, not relevant to the definition.
3. **Select the correct option**: Based on the definitions, select Option B: Catalyst as the correct answer.