In the extraction of $Al$,the chemical used in Serpeck's process is:

Select the correct option regarding the method of separating two sulfide ores by the froth flotation process.
$(1)$ The ratio of water and oil is chosen appropriately.
$(2)$ Some depressants are used for this process.
$(3)$ $HCN$ is a depressant for a mixture of $ZnS$ and $PbS$.
$(4)$ By using a suitable depressant for a mixture of $ZnS$ and $PbS$,only $PbS$ comes up with the froth.

$PbS$ can be separated from $ZnS$ by electrostatic separation. Which property is involved in this method?

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	$c$. $Al_2(SiO_3)_3$

The purification of alumina is called

The process which involves the treatment of the ore with a suitable reagent so as to make it soluble but not the impurities is called: