Which principle is involved in froth flotation?

Bauxite ore is concentrated by

An ore containing the impurity of $FeCr_2O_4$ is concentrated by

$A$ process used for the concentration of ore is

Wolframite ore is separated from tinstone ore by the process of

$4 Ag_{(s)} + 8 CN^{-}_{(aq)} + 2 H_2O_{(l)} + O_{2(g)} \longrightarrow 4 [Ag(CN)_2]^{-}_{(aq)} + 4 OH^{-}_{(aq)}$
The above reaction represents the process of concentration of ore in the extraction of silver. This process is: