The correct order of octane number of butane, pentane, hexane and cycl

The correct order of octane number of butane, pentane, hexane and cyclohexane is

”butane
”butane
”butane
”cyclohexane
This question was previously asked in
UPSC CDS-1 – 2024
Octane number is a measure of a fuel’s resistance to knocking. Branched hydrocarbons and cyclic hydrocarbons have higher octane numbers than straight-chain hydrocarbons with the same number of carbon atoms. The octane number decreases with increasing chain length for straight-chain alkanes.
Comparing the standard (n-) forms:
n-Butane (C4H10) has a higher octane number than n-pentane (C5H12) and n-hexane (C6H14).
n-Pentane has a higher octane number than n-hexane.
Cyclohexane (C6H12), a cyclic alkane, has a higher octane number than the corresponding straight-chain alkane, n-hexane, and typically higher than n-pentane.
The typical order of RON (Research Octane Number) is approximately: n-Butane (~92) > Cyclohexane (~83) > n-Pentane (~62) > n-Hexane (~25).
Thus, the correct order of decreasing octane number is butane > cyclohexane > pentane > hexane.
Octane number is inversely related to chain length for n-alkanes and higher for branched/cyclic structures compared to straight chains.
Octane numbers are determined relative to two reference hydrocarbons: isooctane (2,2,4-trimethylpentane), assigned an octane number of 100 (highly resistant to knocking), and n-heptane, assigned an octane number of 0 (knocks readily). The octane number of a fuel is the percentage of isooctane in a mixture with n-heptane that has the same knocking characteristics as the fuel.
Exit mobile version