Why is the decomposition reaction called the opposite of a combination reaction? Give examples for each.

Hint :A chemical reaction is a process that converts one or more substances, known as reactants, to one or more different substances, known as products. A chemical reaction rearranges the constituent atoms of the reactants to produce various products.

Complete Step By Step Answer:
Decomposition reaction: A decomposition reaction is a chemical reaction that occurs when one reactant breaks down into two or more products.
General Reaction Format:
The general structure of a decomposition reaction is shown below.
 $ AB\text{ }->\text{ }A\text{ }+\text{ }B $
Where AB is the reactant (parent molecule) and $ A $ & $ B $ are the product molecules.
Decomposition reaction examples:
Decomposition reactions occur all around us, but we frequently fail to notice them. The following are some common examples of decomposition reactions.
The chemical equation $ {{H}_{2}}C{{O}_{3}}\text{ }\to {{H}_{2}}O\text{ }+\text{ }C{{O}_{2}} $ represents the decomposition of carbonic acid in soft drinks.
Water electrolysis produces hydrogen and oxygen.
combination reaction: A combination reaction (also known as a synthesis reaction) is a chemical reaction that occurs when two or more elements or compounds (reactants) combine to form a single compound (product). These reactions are represented by equations of the form $ A\text{ }+\text{ }B~\to \text{ }AB $ . A combination reaction occurs when two or more elements combine to form one compound.
The product of a combination reaction between a metal and a nonmetal is an ionic solid. As an example, lithium can react with sulfur to form lithium sulfide. When magnesium burns in the air, its atoms combine with the gas oxygen to form magnesium oxide. The bright flame produced by flares is produced by this specific combination reaction.
Example: $ {{H}_{2}}\left( g \right)\text{ }+\text{ }C{{l}_{2}}\text{ }\to \text{ }2HCl\text{ }\left( g \right) $
The reaction between two or more molecules to form a larger molecule is referred to as the combination reaction, whereas the decomposition reaction is defined as the splitting of larger molecules into two or smaller molecules. This explains why the decomposition reaction is the inverse of the combination reaction.
A combination reaction occurs when two or more reactants combine to form a new single product/compound. A decomposition reaction occurs when a single compound/reactant decomposes into two or more compounds/products.
Thus, the decomposition reaction is called the opposite of a combination reaction.

Note :
Applications of Decomposition Reactions
-Production of cement or calcium oxide.
-Extraction of metals from oxides, chlorides, and other compounds for metallurgical processes
-The alleviation of acid indigestion.
-Welding with thermite.
A wide range of stable ionic compounds can be synthesized using combination reactions. You can predict the formula for these ionic compounds if you know what the most stable ions of various elements are.