What is the role of following ?
(a) Depressant in the froth floatation process.
(b) Silica in the extraction of copper from copper pyrites.
(c ) Cryolite in the metallurgy of aluminium.

Explanation

A depressant controls or depresses the formation of froth with a particular metal sulphide by reacting chemically with it.
(b) Silica acts as the acidic flux and combines with the impurity of ferrous oxide to form ferrous silicate in the form of slag.
` FeO+SiO_(2) to FeSiO_(3) ("slag")`
(c ) In the metallurgy of aluminium, cryolite `(Na_(3)AlF_(6))` is added to lower the melting point of alumina `(Al_(2)O_(3))` and also to increase its conductivity during the electrolytic reduction.