Unsaturated carbon compounds will give a _______ flame with lots of black smoke.

Correct option is A

Unsaturated carbon compounds, like alkenes and alkynes, tend to burn with a yellow flame accompanied by black smoke. Here's a breakdown of the reasons behind this phenomenon:
Complete vs. Incomplete Combustion:
· Complete combustion: When a fuel reacts completely with oxygen (O2) during burning, it produces carbon dioxide (CO2) and water (H2O) along with heat. This typically results in a clean, blue flame.
· Incomplete combustion: If there's insufficient oxygen available for complete combustion, the fuel breaks down only partially. This scenario occurs more frequently with unsaturated hydrocarbons.
· Yellow flame: The un-oxidized carbon particles in the flame get very hot but don't completely burn. These hot particles emit light, causing the yellow color you observe.
· Black smoke: The un-oxidized carbon particles don't burn completely and escape as smoke, giving the flame a sooty appearance.