What does the auto ignition temperature describe?

• A. The temperature above which spontaneous combustion can occur without the use of spark or flame
• B. The temperature required to ignite with a spark
• C. The temperature at which a liquid boils
• D. The temperature at which a material releases flammable vapor

Answer: (A)

Auto ignition temperature is the threshold where a material can ignite in air without any external flame or spark. When heated to this temperature, oxidation inside the material becomes self-sustaining, so ignition happens spontaneously rather than needing an external ignition source. That’s why the choice describing ignition without a spark or flame is the best fit. The other ideas refer to different concepts: needing a spark means external energy is required, the boiling point is about phase change, and releasing flammable vapor relates to vaporization rather than self-ignition.