Setting a fire too or burning substances such as propane or methane in a closed room/building can very easily cause an open flame or fire to the area because they are flammable substances
The only answer that really makes sense here is the first one, properties. I would go with that one.
Depending what you have available there are a few different chemicals you can combine to show an obvious reaction without special equipment. Vinegar and Baking soda is a common mixture. Perhaps something like HCl and NaOH mixed will produce heat.