Answer : An explosive substance is a liquid or a solid which can be burned or ignited easily. It mainly burns with the air and then produces light and heat. It is something that acts as fuel. It is primarily ignited with flammable things that can instantly catch fire and transform into flame. The degree of combustibility depends on the volatility of materials. So, in simple words, combustible materials can be burned very quickly and easily.
There are lots of substances or materials which are examples of combustible substances. Those are wood, cooking gas, coal, cloth, methane, wax, straw, kerosene oil, leaves, charcoal, paper, hydrogen gas, propane, ethanol, and sawdust.