Why are decomposition reactions called the opposite of combination reactions? Write equations for these reactions.

(N/A) Decomposition reactions are those in which a single compound breaks down to form two or more simpler substances. These reactions typically require an input of energy in the form of heat, light, or electricity to proceed.
Combination reactions are those in which two or more substances combine to form a single new substance, often releasing energy in the process.
Therefore, they are considered opposites because decomposition involves breaking down a substance (requiring energy), while combination involves forming a substance (releasing energy).
Decomposition reaction: $2H_2O(l) \xrightarrow{\text{Electrolysis}} 2H_2(g) + O_2(g)$
Combination reaction: $2H_2(g) + O_2(g) \to 2H_2O(l) + \text{Energy}$