Which term is used to describe the byproduct of incomplete combustion that is black and flaky?

The term used to describe the byproduct of incomplete combustion that is black and flaky is soot. Soot is composed primarily of carbon particles that are produced when carbon-based fuels are not burned completely, which often occurs in low-temperature or low-oxygen conditions. This can happen in various scenarios, such as in fireplaces, engines, or during wildfires. The black and flaky nature of soot is a direct result of these unburned carbon particles, which can accumulate and pose health risks, as well as contribute to environmental pollution.

Ash, on the other hand, typically refers to the inorganic residue that remains after a material has been completely burned, which is quite different from soot. Residue can describe any leftover material but is less specific and does not convey the characteristics associated with incomplete combustion specifically. Smog is a type of air pollution that involves a mixture of smoke and fog, often containing various pollutants, but it does not specifically denote the black and flaky characteristic of soot. Thus, soot is the appropriate term for this specific byproduct of incomplete combustion.