Question

Which of the following is a double salt?
(A)Carnallite
(B)Potassium ferrocyanide
(C)Potassium ferricyanide
(D)Nessler’s reagent

Answer 1

Hint :A salt is composed of an anion and a cation. The main difference between a double salt and a complex salt is, a double salt is a combination of two salt compounds whereas a complex salt is a molecular structure composed of one or more complex ions.

Complete Step By Step Answer:
A double salt is a salt containing more than one cation or more than one anion. Examples of double salts are alums and Tutton's salts. Double Salts dissociate into simple ions when they are dissolved in water. In a double salt, normal valency is executed by the metal atom or ion whereas in complexes the negative ions or molecules surrounding the central metal atom are beyond the normal valency. A double salt is formed from a three-component system which comprises two separate salts and water. Double salts are crystalline salts which are composed of a mixture of two simple salts but with a different crystal structure. Double salts are ionisable when they are dissolved in water. So, Carnallite is a double salt.
Therefore, option A is the correct answer.

Note :
A complex salt is a salt which contains one or more complex ions, ions with metal centres and different molecules attached. A salt is a compound composed of oppositely charged ions. A complex ion is a species formed between a central metal ion and one or more surrounding ligands, molecules or ions which contain at least one lone pair of electrons. The formation of a complex ion by adding a complexing agent increases the solubility of the given compound.