A decomposition reaction is a type of chemical reaction where a single compound breaks down into two or more simpler substances. The general form of a decomposition reaction is:
[tex]\[ AB \rightarrow A + B \][/tex]
Let's analyze each of the given reactions to determine which one fits the description.
Option A:
[tex]\[ 2 KClO_3 \rightarrow 2 KCl + 3 O_2 \][/tex]
This reaction shows a single compound, potassium chlorate [tex]\( KClO_3 \)[/tex], breaking down into potassium chloride [tex]\( KCl \)[/tex] and oxygen gas [tex]\( O_2 \)[/tex]. This fits the definition of a decomposition reaction.
Option B:
[tex]\[ 4 Na + O_2 \rightarrow 2 Na_2O \][/tex]
This reaction involves sodium [tex]\( Na \)[/tex] and oxygen [tex]\( O_2 \)[/tex] combining to form sodium oxide [tex]\( Na_2O \)[/tex]. This is a synthesis reaction, not a decomposition reaction.
Option C:
[tex]\[ 2 ZnS + 3 O_2 \rightarrow 2 ZnO + 2 SO_2 \][/tex]
This reaction involves zinc sulfide [tex]\( ZnS \)[/tex] and oxygen [tex]\( O_2 \)[/tex] reacting to form zinc oxide [tex]\( ZnO \)[/tex] and sulfur dioxide [tex]\( SO_2 \)[/tex]. This is a combustion reaction, not a decomposition reaction.
Option D:
[tex]\[ 2 NaBr + CaF_2 \rightarrow 2 NaF + CaBr_2 \][/tex]
This reaction is a double displacement reaction where sodium bromide [tex]\( NaBr \)[/tex] and calcium fluoride [tex]\( CaF_2 \)[/tex] exchange ions to form sodium fluoride [tex]\( NaF \)[/tex] and calcium bromide [tex]\( CaBr_2 \)[/tex]. This is not a decomposition reaction.
Based on the definitions and the analysis of each reaction, the correct answer is:
[tex]\[ \boxed{A} \][/tex]
