Define fuel. List any two characteristics that you would look for in a good fuel.

A fuel is that substance which, on combustion can provide sufficient energy in a convenient form for sustained use over a long period of time.
Two important characteristics of a good fuel are:
(i) The fuel is available easily at an economic price and can be conveniently transported and stored.
(ii) What is the amount and rate of release of heat energy by the fuel on burning and whether any smoke is produced or not.