Magnetic separation is used for increasing the concentration of which of the following ores?

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

In the process of extracting alumina from bauxite,bauxite is concentrated by $......$.

The function of potassium ethyl xanthate in the froth floatation process is to make the ore

Froth floatation process is used for the concentration of the ore of

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