Which factor explains why coal dust is explosive?
temperature
surface area
concentration
addition of catalyst

The answer to the question stated above is surface area. 
Coal dusts are fine powdered form of coal, which are formed by crushing, grinding, or pulverizing of coal. They can be created during mining, transportation, or by mechanically handling coal because of its brittle nature.
The surface area of the coal dust explains why it is explosive.

The answer is a i believe