Naphthalene burns with a yellow sooty flame. This is because
there is incomplete combustion
The correct answer is Option 2.
Key Points
Saturated hydrocarbons will generally give a clean flame, while unsaturated carbon compounds will give a yellow, sooty flame with a lot of black smoke.
Naphthalene is an unsaturated compound. The proportion of carbon in unsaturated hydrocarbons is higher than that in saturated hydrocarbons. That is, the carbon-to-hydrogen ratio is high.
As a result, some unburnt carbon particles are also formed during the combustion of unsaturated compounds.
In the flame, these unburnt hot carbon particles emit yellow light, which makes the flame appear yellow. Therefore, naphthalene burns with a yellow flame.
However, limiting the supply of air results in incomplete combustion of even saturated hydrocarbons, giving a sooty flame.
Therefore, the most appropriate reason for a yellow sooty flame is incomplete combustion.
The correct answer is Option (2).
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