An organic compound burns with a sooty flame, it is an unsaturated compound.

Explanation:

i. When an unsaturated compound is burned it will give a yellow flame with lots of smoke.

ii. This is the sooty flame.

iii. This happens due to incomplete combustion.

iv. When the compound is burned in a limited supply of oxygen, it will release CO (Carbon monoxide) in place of CO₂ resulting in incomplete combustion.

Hence, unsaturated compound gives sooty flame due to incomplete combustion.