Question

All combustible substance are not fuels .why?

Answer 1

Answer:

here is your answer

Explanation:

Combustible substances are those which can burn.It is not necessary that they will produce a large amount of heat without leaving any residue on combustion.Hence all fuels are combustible but all combustible substances are not fuels.

hope it's helpful......

Answer 2

$\huge\mathtt\red{Answer}$

All combustible substance are not fuels because it is not necessary that combustible substance will produce large amount of heat. If some combustible substance do so they will leave a residue on the substance.

Thus, every combustible substance is not a fuel but every fuel is a combustible substance.