[Giving medal] To create hydrogen and oxygen from water, you would need to perform which type of reaction?
A. Synthesis
B. Decomposition
C. Single replacement
D. Double replacement

Question

[Giving medal] To create hydrogen and oxygen from water, you would need to perform which type of reaction?
  A. Synthesis 	
  B. Decomposition 	
  C. Single replacement 	
  D. Double replacement

jfraser · Answer

those choices are 4 of the 5 most common reaction classes, or types. The wording of the problem actually tells you everything you need. What you have is a reaction that has the general format of:

$$water \rightarrow oxygen + hydrogen$$You start with a single reactant that breaks up into multiple products. What kind of reaction does that?