In froth floatation process for the purification of ores, the particles of ore float because :

Froth floatation process works on the principle of difference in wettability between the ore and the gangue particles.

Particles that can be easily wetted by water are called hydrophilic, while particles that are not easily wetted by water are called hydrophobic. Hydrophobic particles have a tendency to form a separate phase in aqueous media. 

In froth floatation process, first the powdered ore is added to water with frothing agent (pine oil) along with collecting agent (sodium ethyl xanthate) is added. Cresol and aniline are added to stabilize the froth. A vigorous stream of air is passed to agitate the mixture, as a result, the particles of sulphide ore stick to the oil and rise to the surface in the form of froath. However, the gangue particles are wetted by water and settled down at the bottom of the tank. Thus the purification of the ores occur by this method.

Option A is the valid answer.