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Q107 (CAPF/2026) Science & Technology › Basic Science (Physics, Chemistry, Biology)

Consider the following statements in the light of octane number and cetane number of fuels :
1. Cetane number is used for gasoline and octane number is used for diesel.
2. Octane number of n-hexadecane is 100 and cetane number of isooctane is 100.
Which of the statements given above is/are correct?

Result
Your answer: —  ·  Correct: D

Explanation

Both statements are incorrect due to the reversal of terms and properties. Statement 1 is false because the Octane number is used to measure the anti-knock quality of gasoline (petrol), whereas the Cetane number is used to measure the ignition quality and combustion speed of diesel fuel.

Statement 2 is false because it swaps the reference standards for the two scales. In the octane rating system, isooctane is assigned a value of 100 (representing high resistance to knocking), while n-heptane is 0. In the cetane rating system, n-hexadecane (also known as cetane) is assigned a value of 100 (representing very short ignition delay), while heptamethylnonane is used as the low-quality reference. Therefore, n-hexadecane is the benchmark for cetane, not octane.

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