Question

what is difference between combination and decomposition reaction with example

Answer 1

In combination reaction 2 or more reactant combine to form a single product e.g : C + O2 -> CO2 and In a decomposition reaction 1 reactant is broken down into two or more products e.g : C12H22O11 -> 12C + 11H2O

Answer 2

Chemical reactions are the reactions in which some of the molecules react to form new molecules. On the basis of reactions, they can be divided in to different types.  

Combinations reactions and decomposition reactions are just opposite to each other.

Combination reactions involve combination of "two or more" substances to form one substance whereas decomposition reactions break one molecule into "two or more" basic components.  

Example for combination reaction:

$\mathrm{H}_{2}+\mathrm{Cl}_{2} \rightarrow 2 \mathrm{HCl}$

Example for decomposition reaction:

$\mathrm{CaCO}_{3}+\mathrm{heat} \rightarrow \mathrm{CaO}+\mathrm{CO}_{2}$

Hence, they are considered as opposite reactions.