From the following, the ores that are concentrated by froth flotation are:

 a. Haematite b. Galena c. Copper pyrites d. Magnetite

Choose the correct option:
1. a and b
2. b and c
3. c and d
4. a and d

HINT: Sulphide ores are extracted by froth floatation method.
Explanation:
The basic principle applied in the process of Froth Flotation is the difference in the wetting ability of the ore and remaining impurities.
Haematite $\left({\mathrm{Fe}}_{2}{\mathrm{O}}_{3}\right)$ and magnetite $\left({\mathrm{Fe}}_{3}{\mathrm{O}}_{4}\right)$ are oxide ores while galena $\left(\mathrm{PbS}\right)$ and copper pyrites  are sulphide ores. As we know sulphide ores are extracted by using froth floatation method.
Hence, (b) and (c) are the correct choices.