A substance which itself is not a catalyst but………….. .the reactivity of a catalyst is called a promoter and the one which reduces the activity is called…………for the catalyst.

Answer

To solve the question, we need to fill in the blanks with the correct terms related to catalysts.

1. **Understanding the Role of Promoters**:
- A promoter is a substance that enhances or increases the reactivity of a catalyst. It does not act as a catalyst itself but supports the catalyst in facilitating a reaction more effectively.
- Therefore, the first blank should be filled with the word "increases".

2. **Understanding the Role of Poisons**:
- A poison, in the context of catalysis, is a substance that decreases or inhibits the activity of a catalyst. It can interfere with the catalyst's ability to facilitate a reaction, thus slowing down or stopping the reaction.
- Hence, the second blank should be filled with the word "poison".

**Final Answers**:
- A substance which itself is not a catalyst but **increases** the reactivity of a catalyst is called a promoter and the one which reduces the activity is called **poison** for the catalyst.