Classifying reactions by what the atoms do

chem 3a exam #3

synthesis reaction

two simpler substances combine to make a more complex substance
A+B → AB

Decomposition reaction

a complex substance decomposes to form simpler substances.
AB → A + B

The following reaction is a?

2 H20 → 2 H2 + 02

A) synthesis reaction
B) decomposition reaction
C) displacement reaction
D) double displacement reaction 

B) decomposition reaction 

Single-displacement reaction

one element displaces another in a compound.
A + BC → AC + B

double-displacement reaction

two elements or groups of elements in two different compounds exchange places to form two new compounds
AB + CD → AD + BC