Identify the product formed when bauxite ore is treated with sodium hydroxide?

Chemical leaching is useful in the concentration of

For which ore of the metal,froth floatation method is used for concentration?

The correct statements regarding the froth floatation method in metallurgy are:
$I$. Used for the purification of sulphide ores
$II$. Used for the roasting of sulphide ores
$III$. It is based on the relative densities of gangue and ore particles
$IV$. It is based on the difference in the wetting properties of gangue and ore particles in frothing agent and water

What are the various methods used for the concentration of an ore?

The substance added to the ore to remove impurities is known as........