Which one of the following methods is used in the concentration of sulphide ore ?

Froth flotation is a process for selectively separating hydrophobic materials from hydrophilic. This is used in several processing industries, the single most important operation used for the recovery and upgrading of sulphide ores.
It is the process in which air bubbles are introduced into a mixture of finely divided ore or other material with water and a chemical that aids attachment of the bubbles to the particles of the desired material and its recovery as a froth.