<P> Due to the free state nature of A and B, all single displacement reactions are also oxidation - reduction reactions, where the key event is the movement of electrons from one reactant to another . When A and B are metals, A is always oxidized and B is always reduced . Since halogens prefer to gain electrons, A is reduced (from 0 to − 1) and B is oxidized (from − 1 to 0) when A and B represent those elements . </P> <P> A and B may have different charge as ions and therefore some balancing of the equation may be necessary . For example, the reaction between silver nitrate, AgNO (which contains an Ag ion), and zinc, Zn, forms silver, Ag, and zinc nitrate, Zn (NO) (which contains a Zn ion). </P> <Dl> <Dd> 2AgNO (aq) + Zn (s) → 2Ag (s) + Zn (NO 3) (aq) </Dd> </Dl> <Dd> 2AgNO (aq) + Zn (s) → 2Ag (s) + Zn (NO 3) (aq) </Dd>

Which one of the following does not describe a single-displacement reaction