COMBINE to FORM a single compound. Such reactions may be REPRESENTED by equations of the following form: X + Y → XY.Decomposition reactions are a type of chemical reaction that involves breaking down a compound into smaller compounds or individual elements.A single-displacement reaction, ALSO known as a single-replacement reaction, is a reaction by which one element replaces other element in a compound.A double displacement reaction, also known as a double replacement reaction or metathesis, is a type of chemical reaction where two compounds react, and the positive ions (action) and the negative ions (anion) of the two reactants switch places, forming two new compounds or products.Hence, 1 is the CORRECT option.