What occurs to flammable materials in the presence of air?

Flammable materials, in the presence of air, are capable of burning when exposed to a sufficient source of heat, such as a spark or flame. This is because most flammable materials require three elements to ignite: fuel (the flammable material), heat (an ignition source), and oxygen (from the air) to sustain combustion. When these materials are simply present in an atmosphere with air, they do not ignite or change state until an ignition source is applied.

The option stating that flammable materials spontaneously combust is incorrect because spontaneous combustion is rare and typically requires specific conditions, such as prolonged exposure to heat without adequate ventilation, rather than just the presence of air.

Similarly, the notion that flammable materials remain unchanged inaccurately suggests that these materials do not have the potential to combust, which overlooks the critical role of an ignition source. The idea that they dissolve in the air is not applicable, as flammable materials do not dissolve in air; they remain in solid or liquid form until ignited. Therefore, the correct answer explains that these materials stay in their original state until they encounter an ignition source.