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General formula for Aluminum alums:-
(A) $ [M{({H_2}0)_6}][Al{({H_2}O)_6}{[S{O_4}]_3} $
(B) $ [M{({H_2}0)_4}][Al{({H_2}O)_4}{[S{O_4}]_4} $
(C) $ [M{({H_2}0)_4}][Al{({H_2}O)_6}{[S{O_4}]_2} $
(D) $ [M{({H_2}0)_6}][Al{({H_2}O)_6}{[S{O_4}]_2} $

Last updated date: 19th Jul 2024
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Hint :Double salt is a kind of salt which generally contains cations and anions more than one in the same salt. Alums are a kind of double salt which are hydrated and contain aluminum along with a monovalent cation. The cations are generally potassium and ammonium known as potash alum, ammonium alum.

Complete Step By Step Answer:
Alums are classified as inorganic compounds which are hydrated double salts of sulphate and aluminum.
General formula for alums are: $ [M{({H_2}0)_6}][Al{({H_2}O)_6}{[S{O_4}]_2} $
In which M is a monovalent atom mainly sodium, potassium, ammonium.
Alums are highly soluble in water, they crystallize in octahedral structure.
Potash alum: In potash alum the monovalent cation is potassium chemically called potassium aluminum sulphate. The physical form is white crystal form. Chemical formula $ KAl{(S{O_4})_2}.12{H_2}O $
Ammonium alum: It is ammonium sulphate alum. Chemical formula $ N{H_3}Al{(S{O_4})_2}.12{H_2}O $ .
Alums like potash alum generally known as “fitkari” is used to treat water, it acts as coagulants which when added to impure water, increase the size of impurities and makes them settle down in the container which can be later filtered.
Option (D) $ [M{({H_2}0)_6}][Al{({H_2}O)_6}{[S{O_4}]_2} $ is the correct choice.

Note :
Alums have wide applications in our day to day lives, they are also used as antiseptics. They are used as Pickling agents, helps to remove impurities from water. They fix the dyes on the fabric and alums are used as dyeing agents in industries.