Which characteristic best identifies a decomposition reaction? a single compound as a reactant a single compound as a product an element and a compound as reactants an element and a compound as products

Answer is: a single compound as a reactant

Decomposition is reaction where one substance is broken down into two or more simpler substances.

1) Electrolysis of water is the decomposition reaction, because from one molecule (water) two molecules (hydrogen and oxygen) are produced. Water is separated into two molecules.

2) Chemical decomposition is the separation of a carbonic acid into water and carbon dioxide: H₂CO₃ → CO₂ + H₂O.

i believe you are right for all except the 3rd ( look at sqdancefan his answer is much better)