Question

Which type of hydrocarbon gives sooty flame on burning?

Answer 1

Unsaturated hydrocarbons like ethyne, also known as acetylene, burn to produce a yellow, sooty flame due to incomplete combustion in air. The flame is sooty because the percentage of carbon is comparatively higher than that of alkanes and so does not get completely oxidized in air

Answer 2

Saturated hydrocarbons  will give a clean flame wheras unsaturated  carbon  compounds  ie;  carbon compounds having double or triple  bonds  will  give a yellow sooty flame with lots  of  black  smoke.