Leaching of $Ag_2S$ is carried out by heating it with a dilute solution of

Chemical leaching is useful in the concentration of

Given below are two statements :-
Statement $I$: In froth floatation method,a rotating paddle agitates the mixture to draw air into it.
Statement $II$: Iron pyrites are generally avoided for the extraction of iron due to environmental reasons.
In the light of the above statements,choose the correct answer from the options given below :-

During initial treatment,preferential wetting of ore by oil and gangue by water takes place in

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:

Bauxite containing impurities of iron oxide is purified by