A catalytic poison renders the catalyst ineffective beacause :

Options

A. It is perferentiallly adsorbed on the catalyst
B. It adsorbs the molecules of the reactants
C. It combines chemically with the catalyst
D. it combines chemically with one of the reactants

Answer

To solve the question "A catalytic poison renders the catalyst ineffective because:", we can analyze the options provided and determine the correct answer step by step.

### Step 1: Understand the Role of Catalysts
Catalysts are substances that increase the rate of a chemical reaction without being consumed in the process. They work by providing an alternative reaction pathway with a lower activation energy.

### Step 2: Define Catalytic Poison
A catalytic poison is a substance that decreases or inhibits the activity of a catalyst. It can do this by interfering with the catalyst's ability to facilitate the reaction.

### Step 3: Analyze the Options
- **Option A**: "Catalytic poison renders the catalyst ineffective because it is preferentially adsorbed on the catalyst."
- This suggests that the poison attaches itself to the catalyst's surface, blocking the active sites necessary for the reaction to occur.

- **Option B**: "It adsorbs the molecule of the reactants."
- This implies that the poison interacts with the reactants instead of the catalyst, which does not directly explain how the catalyst becomes ineffective.

- **Option C**: "It combines chemically with the catalyst."
- This indicates a chemical reaction between the poison and the catalyst, which could render the catalyst inactive, but it does not specifically address the mechanism of adsorption.

- **Option D**: "It combines chemically with one of the reactants."
- This suggests that the poison interacts with the reactants rather than the catalyst, which does not explain the catalyst's ineffectiveness.

### Step 4: Determine the Best Answer
The most appropriate answer is **Option A**, as it directly explains that the catalytic poison is preferentially adsorbed on the catalyst, preventing the catalyst from interacting with the reactants and thus rendering it ineffective.

### Conclusion
The correct answer is **A. Catalytic poison renders the catalyst ineffective because it is preferentially adsorbed on the catalyst.**

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