How is the explosive range defined?

The explosive range is defined as the concentration of flammable vapors in the air that can ignite and produce an explosion. When considering the definition provided, the correct focus is on the mixture of flammable vapors and air, which is crucial for combustion to occur.

The mixture must contain a specific percentage of flammable vapors — too little and there isn't enough fuel to support combustion; too much, and there isn't enough oxygen to sustain the reaction. This balance creates the parameters of the explosive range, which identifies the conditions under which a flame or explosion can take place.

In contrast, the other options do not accurately describe the explosive range. The inclusion of water or solid fuels does not align with the fundamental requirements for ignitability in terms of vapor concentration. Therefore, the mixture of flammable vapors and air is essential for understanding explosive limits.