Question

Why Acetylene burns with a sooty flame​

Answer 1

The unsaturated hydrocarbons l[alkene and alkyne ] burn in air with a yellow sooty flame producing black smoke.
for example: Ethyne burns in air with a sooty flame because the percentage of carbon in unsaturated hydrocarbon is comparatively higher than alkane which does not get oxidised completely in the presence of air.
Air contains only 21% of O2 which is not sufficient for complete combustion.
But if unsaturated hydrocarbons are burnt in pure O2 than complete combustion can take place.

Answer 2

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The carbon to hydrogen $\bold{ratio}$ in acetylene is 1.

Which is high, due to which $\bold{incomplete}$ combustion takes place and acetylene burns with a $\bold{sooty\:flame.}$

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