Question

Which of the following is a combustion reaction?

• A. Burning of petrol
• B. Boiling of water
• C. Melting of wax
• D. None of these

Answer 1

Answer: (A)

Combustion reactions always involve molecular oxygen $O_2$. Anytime anything burns (in the usual sense), it is a combustion reaction. Combustion reactions are almost always exothermic (i.e., they give off heat). For example: When wood burns, it must do so in the presence of $O_2$ and a lot of heat is produced.