When methane burns, the formula of which is CH4, carbon dioxide and water are formed.

CH4 + 2O2 = CO2 + 2H2O
Can this reaction be classified as one of the types you have studied:
a) by the composition and number of reagents and reaction products; You can’t. A simple substance is among the reagents and absent among the reaction products.
b) on the basis of absorption or release of heat? Can. All combustion reactions are exothermic, that is, they are accompanied by the release of heat.

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