Why is the concentration of ore performed?

Which of the following is used as a froth stabilizer in the froth flotation process?

Which method is used for the concentration of the tin ore containing $FeCrO_4$?

The ore that is concentrated by froth floatation process is

Difference in density is the basis of

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.