Which of the following describes a material that does not combust but can smolder?

An ember is a solid material that can maintain heat and often glows red as it continues to smolder, despite not actively combusting. Embers are typically remnants of burning organic materials, like wood, and can ignite nearby combustible materials if they are in close proximity. The process of smoldering occurs when there is insufficient oxygen to sustain open flame, allowing the ember to continue releasing heat and smoke while not being in full combustion.

Cinders, soot, and ash represent different stages or byproducts of combustion. Cinders can be considered similar to embers but are often less likely to retain enough heat to smolder. Soot is a fine black powder that forms from incomplete combustion and is primarily composed of carbon particles, while ash is the non-combustible residue left after a material has completely burned. Neither soot nor ash will smolder as they do not possess the ability to retain heat in the same manner as embers. Thus, ember is the appropriate choice that captures the essence of being a material that can smolder without combusting.