Which of the following is a decomposition reaction? A. CH4 + 2O2 CO2 + 2H2O B. 2Mg + O2 2MgO C. CaCO3 CaO + CO2 D. 2H2O + 2Na 2NaOH + H2

The decomposition reaction is the one taking place in C.

CaCO₃ → CaO + CO₂

In a decomposition reaction, a single reactant is made to break down by providing a change in external conditions, such as the addition of heat, to produce a different product. This decomposition of calcium carbonate occurs due to the addition of heat energy, and is called a thermal decomposition.