Spontaneous combustion occurs when a substance ignites on its own, without an external ignition source, due to internal heat generation from oxidation or other chemical reactions.

Analyzing the options:

• Coal mine fires can start spontaneously from the oxidation of coal dust.
• LPG requires a spark or flame to ignite; it is not spontaneous.
• Dry white phosphorus reacts with air, igniting spontaneously at room temperature: $4P+5{\mathrm{O}}_2\to 2{\mathrm{P}}_2{\mathrm{O}}_5$ + heat.

Therefore, only the first and third options are correct examples. "All of these" is incorrect because LPG does not ignite spontaneously.

Final Answer: Dry white phosphorous liberates white fumes on exposure to air.