Naphthalene burns with a yellow sooty flame. This is because

Naphthalene (C10H8) is an aromatic hydrocarbon characterized by a high carbon-to-hydrogen ratio. When it burns, it produces a yellow, sooty flame primarily due to incomplete combustion [2]. Incomplete combustion occurs when there is an insufficient supply of oxygen to fully oxidize the carbon atoms into carbon dioxide. This process results in the formation of soot, which consists of solid carbon particles or aerosols . These unburnt carbon particles are heated within the flame and glow, giving the flame its characteristic yellow, luminous appearance [2]. While saturated hydrocarbons typically burn with a clean blue flame, unsaturated and aromatic compounds like naphthalene naturally produce more smoke and soot because their high carbon content requires more oxygen for complete combustion than is typically available in ambient air [1]. Therefore, the yellow sooty flame is a direct consequence of the presence of unburnt carbon particles resulting from incomplete combustion.

Sources

1. [1] Science , class X (NCERT 2025 ed.) > Chapter 4: Carbon and its Compounds > Activity 4.4 > p. 69
2. [2] Science , class X (NCERT 2025 ed.) > Chapter 4: Carbon and its Compounds > Why do substances burn with or without a flame? > p. 70