Which statement correctly differentiates flash point and autoignition temperature?

Which statement correctly differentiates flash point and autoignition temperature?

• A. Autoignition temperature is the temperature at which vapors can momentarily ignite.
• B. Flash point is the ignition temperature that requires an external spark.
• C. Flash point is the lowest temperature at which vapors can momentarily ignite; autoignition is the temperature at which a material will ignite without an external ignition source.
• D. Autoignition occurs only at room temperature.

Answer: (C)

Ignition can happen in two different ways: with an external heat source or on its own when a material reaches a high enough temperature. The flash point is the lowest temperature at which vapors above a liquid can form an ignitable mixture with air and actually ignite when an ignition source is present. Autoignition temperature is the temperature at which the material will ignite without any external ignition source, simply due to being heated to that point. That is why the statement matches best: it defines flash point as the lowest temperature at which vapors can momentarily ignite and autoignition as the temperature at which ignition occurs without an external ignition source. The other options mix up these ideas—one incorrectly frames autoignition as the vapors momentarily igniting, another suggests flash point is just an ignition temperature needing a spark without emphasizing the vapors and the lowest-temperature criterion, and another wrongly claims autoignition only happens at room temperature.

Ignition can happen in two different ways: with an external heat source or on its own when a material reaches a high enough temperature. The flash point is the lowest temperature at which vapors above a liquid can form an ignitable mixture with air and actually ignite when an ignition source is present. Autoignition temperature is the temperature at which the material will ignite without any external ignition source, simply due to being heated to that point.

That is why the statement matches best: it defines flash point as the lowest temperature at which vapors can momentarily ignite and autoignition as the temperature at which ignition occurs without an external ignition source. The other options mix up these ideas—one incorrectly frames autoignition as the vapors momentarily igniting, another suggests flash point is just an ignition temperature needing a spark without emphasizing the vapors and the lowest-temperature criterion, and another wrongly claims autoignition only happens at room temperature.