Bauxite ore is concentrated by

Which method is used for the concentration of aluminum ore?

The pair of oxides,which can be leached out when powdered bauxite containing certain impurities is digested with a concentrated solution of $NaOH$ at $473-523 \ K$ temperature and $35-36 \ bar$ pressure,are:

Match the method of concentration of the ore in column $I$ with the ore in column $II$ and select the correct alternate :

$I$	$II$
$X$. Magnetic separation	$a$. $Ag_2S$
$Y$. Froth floatation	$b$. $FeCr_2O_4$
$Z$. Gravity separation	$c$. $Al_2(SiO_3)_3$

Ores like magnetite or tungstates in tin ores are concentrated by

Difference in density is the basis of