Which factor influences the flash point of a substance?

The flash point of a substance is influenced by the presence of an ignition source, as this defines the temperature at which the substance will ignite when mixed with air in sufficient proportions. The flash point is the lowest temperature at which vapors of a substance can ignite when an ignition source, like a spark or flame, is introduced.

Factors such as the chemical composition and volatility of the materials involved also play crucial roles in determining flash points, but the ignition source is critical because, without it, a substance can produce flammable vapors without actually igniting. This makes understanding flash points vital for safety in handling and storing hazardous materials, particularly in environments where ignition sources may be present.

Other options like the weight of the substance, color, or method of storage do not directly affect the flash point in the same way, as these characteristics do not change the temperature at which vapors become flammable in the presence of an ignition source.