Depressant used in the concentration of an ore containing $ZnS$ and $PbS$ is

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:

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 :-

The froth flotation process used for the concentration of sulphide ore:

In the froth floatation process for the purification of ores,the ore particles float because

If bauxite contains $SiO_2$ as an impurity,which of the following methods can be used for its purification?