Explanation:

A single-displacement reaction, also known as single replacement reaction or exchange reaction, is a chemical reaction in which ONE element is replaced by another in a compound.[1][2][3]

It can be represented generically as:

{\displaystyle {\ce {A + B-C -> A-C + B}}}{\displaystyle {\ce {A + B-C -> A-C + B}}}

where

{\displaystyle {\ce {A}}}{\displaystyle {\ce {A}}} and {\displaystyle {\ce {B}}}{\displaystyle {\ce {B}}} are different metals (or any element that forms cation like hydrogen) and {\displaystyle {\ce {C}}}{\displaystyle {\ce {C}}} is an anion;[2] or

{\displaystyle {\ce {A}}}{\displaystyle {\ce {A}}} and {\displaystyle {\ce {B}}}{\displaystyle {\ce {B}}} are halogens and {\displaystyle {\ce {C}}}{\displaystyle {\ce {C}}} is a cation.[2]

This will most often occur if {\displaystyle {\ce {A}}}{\displaystyle {\ce {A}}} is more reactive than {\displaystyle {\ce {B}}}{\displaystyle {\ce {B}}}, thus giving a more stable product.

In the first case, when {\displaystyle {\ce {A}}}{\displaystyle {\ce {A}}} and {\displaystyle {\ce {B}}}{\displaystyle {\ce {B}}} are metals, {\displaystyle {\ce {BC}}}{\displaystyle {\ce {BC}}} and {\displaystyle {\ce {AC}}}{\displaystyle {\ce {AC}}} are usually aqueous compounds (or very rarely in a molten state) and {\displaystyle {\ce {C}}}{\displaystyle {\ce {C}}} is a spectator ion (i.e. remains unchanged).[1]

{\displaystyle {\ce {A(s) + \underbrace{B+(aq) + C^{-}(aq)}_{BC(aq)}-> \underbrace{A+(aq) + C^{-}(aq)}_{AC(aq)}+ B(s)}}}{\displaystyle {\ce {A(s) + \underbrace{B+(aq) + C^{-}(aq)}_{BC(aq)}-> \underbrace{A+(aq) + C^{-}(aq)}_{AC(aq)}+ B(s)}}}

When a copper wire is dipped in a silver nitrate solution, copper displaces silver and solid silver precipitates out: Cu + AgNO₃ → Cu(NO₃)₂ + Ag↓

File:Single Displacement AGNO3 and Cu.ogvPlay media

In the REACTIVITY series, the metals with the highest propensity to donate their electrons to react are listed first, followed by less reactive ones. Therefore, a metal higher on the list can displace anything below it. Here, is a condensed version of the same: [1]

{\displaystyle {\ce {K>Na>CA>Mg>Al>\color {grey}C>Zn>Fe>\color {grey}H>Cu>Ag>Au}}}{\displaystyle {\ce {K>Na>Ca>Mg>Al>\color {grey}C>Zn>Fe>\color {grey}H>Cu>Ag>Au}}}

(Hydrogen and Carbon are non-metals that form cations.)

Similarly, the halogens with the highest propensity to acquire electrons are the most reactive. The activity series for halogens is: [1][2][3]{\displaystyle {\ce {F2>Cl2>Br2>I2}}}{\displaystyle {\ce {F2>Cl2>Br2>I2}}}

Due to the free state nature of {\displaystyle {\ce {A}}}{\displaystyle {\ce {A}}} and {\displaystyle {\ce {B}}}{\displaystyle {\ce {B}}}, single displacement reactions are also redox reactions, involving the transfer of electrons from one REACTANT to another.[4] When {\displaystyle {\ce {A}}}{\displaystyle {\ce {A}}} and {\displaystyle {\ce {B}}}{\displaystyle {\ce {B}}} are metals, {\displaystyle {\ce {A}}}{\displaystyle {\ce {A}}} is always oxidized and {\displaystyle {\ce {B}}}{\displaystyle {\ce {B}}} is always reduced. Since halogens prefer to gain electrons, {\displaystyle {\ce {A}}}{\displaystyle {\ce {A}}} is reduced (from {\displaystyle {\ce {0}}}{\displaystyle {\ce {0}}} to {\displaystyle {\ce {-1}}}{\displaystyle {\ce {-1}}}) and {\displaystyle {\ce {B}}}{\displaystyle {\ce {B}}} is oxidized (from {\displaystyle {\ce {-1}}}{\displaystyle {\ce {-1}}} to {\displaystyle {\ce {0}}}{\displaystyle {\ce {0}}}).