An automobile engine fuel has cetane number of 80. Which of the following statements is/are true ?

Options

A. (a) Fuel contains `80%` of `alpha`-methyl naphthalene and `20%` of `C_(16)H_(34)` .
B. (b) Fuel contains `80%` of centane and `20%` of `alpha`-methyl naphthalene.
C. (c) Knocking property of the given fuel compared to the knocking property of a fuel with cetane number of 90 is high.
D. (d) Centane number determines the quality of diesel fuel in terms of ignition properties.

Explanation

To determine which statements regarding an automobile engine fuel with a cetane number of 80 are true, we will analyze the given information step by step.

### Step 1: Understand the Cetane Number
The cetane number is a measure of the ignition quality of diesel fuel. It indicates how quickly the fuel will ignite when injected into the engine. A higher cetane number means the fuel ignites more readily, leading to better engine performance.

**Hint:** Remember that a cetane number of 80 means the fuel has good ignition properties.

### Step 2: Interpret the Cetane Number
A cetane number of 80 suggests that the fuel contains 80% cetane. This means that the remaining 20% could be other components, such as alpha-methyl naphthalene or other hydrocarbons.

**Hint:** The cetane number is often interpreted as the percentage of cetane in the fuel.

### Step 3: Evaluate the Statements
Now, we will evaluate the statements provided in the question based on our understanding of the cetane number.

1. **Statement A:** "80% of alpha-methyl naphthalene."
- This statement is incorrect because the fuel has 80% cetane, not alpha-methyl naphthalene.

2. **Statement B:** "Fuel contains 80% of cetane and 20% of alpha-methyl naphthalene."
- This statement is correct. Since the cetane number is 80, it implies that the fuel consists of 80% cetane and the remaining 20% could be other components.

3. **Statement C:** "Knocking property of the given fuel compared to the knocking property of a fuel with cetane number 90 is higher."
- This statement is incorrect. A fuel with a higher cetane number (like 90) has better ignition properties and thus would have a lower knocking tendency compared to a fuel with a cetane number of 80.

4. **Statement D:** "Cetane number determines the quality of diesel fuel in terms of ignition property."
- This statement is correct. The cetane number is indeed a measure of the ignition quality of diesel fuel.

### Conclusion
Based on the evaluation of the statements:
- **True Statements:** B and D
- **False Statements:** A and C

### Final Answer
The correct options are B and D.

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