What is the role of :
( i) Depressants in froth floatation ?
(b) Carbon monoxied in Mond's process ?
( c) Concentrated sodium hydroxide in leaching of alumina from bauxite ?

Explanation

See Q.12 (iii) ,Paper - 2015 ,Outside Delhi ,Set-i[Page 304]
( b) See Q.13 (i) Paper - 2012 ,Delhi Board ,Set-I [Page 140]
(c ) Bauxite `(Al_2O_3.2H_2O)` contains more amount of `Fe_2O_3` as imortant than `SiO_2`impurity .Now since iron oxide is basic and aluminium oxide is amphoteric ,using NaOH dissolve aluminium oxide has silicates ,but iron oxide remain unreacted and insoluble which can be easily separated by filtration .