Which ore is concentrated by the froth flotation process?

Chemical leaching is useful in the concentration of

Sulphide ores of metals are usually concentrated by froth floatation process. Which one of the following sulphide ores offers an exception and is concentrated by chemical leaching?

In the leaching of alumina from bauxite,the ore impurity expected to leach out in the process by reacting with $NaOH$ is:

Which of the ores mentioned in the table can be concentrated by the magnetic separation method?

Metal	Ores and Composition
$Aluminium$	$Bauxite: AlO_{x}(OH)_{3-2x} (0 < x < 1)$; $Kaolinite: [Al_{2}(OH)_{4}Si_{2}O_{5}]$
$Iron$	$Haematite: Fe_{2}O_{3}$; $Magnetite: Fe_{3}O_{4}$; $Siderite: FeCO_{3}$; $Iron pyrites: FeS_{2}$
$Copper$	$Copper pyrites: CuFeS_{2}$; $Malachite: CuCO_{3} \cdot Cu(OH)_{2}$; $Cuprite: Cu_{2}O$; $Copper glance: Cu_{2}S$
$Zinc$	$Zinc blende or Sphalerite: ZnS$; $Calamine: ZnCO_{3}$; $Zincite: ZnO$

Explain the concentration of ore by Magnetic Separation.