Question

there are only three elements in fuel which on combustion gives energy
A.carbon, Oxygen and sulphur B.carbon, hydrogen and sulphur C.carbon, nitrogen and sulphur
D. air, Co2 and sulphur​

Answer 1

A. Carbon , Oxygen , Sulphur is the correct answer .

Answer 2

The three elements which on combustion give energy are B.carbon, hydrogen and sulphur

Combustion

• Combustion is a chemical reaction which occurs in the presence of oxygen and produces energy in the form of heat and light. It is an exothermic reaction.
• A fuel contains hydrogen, oxygen and carbon. Hydrogen and carbon exist in the form of a compound called hydrocarbons.
• The oxygen works by oxidizing carbon to carbon dioxide and hydrogen to water( $H_{2}$O)
• Here is the combustion reaction for a hydrocarbon called propane(   $C_{3}H_{8}$):

                   $C_{3}H_{8}$+$5O_{2}$ → $3CO_{2} + 4H_{2}O$

Incorrect options

• A.carbon, Oxygen and sulphur is incorrect because sulphur is not flammable
• C.carbon, nitrogen and sulphur is also incorrect since sulphur and nitrogen are not flammable.
• D. air, Co2 and sulphur​ is incorrect because $CO_{2}$  extinguishes fire.