Answer: Option C
:
C and D
In a decomposition reaction, the reactant breaks into two or more simple products. So, the reactions of calcium carbonate and potassium chlorate to form products are examples of decomposition reaction. 
The reaction between zinc and hydrochloric acid is a displacement reaction as zinc is displacing hydrogen.
The reaction between hydrogen and chlorine is a combination reaction as the reactants are combining to form hydrogen chloride.