Question

Which answers all the tests of constituent ions?
(A) Mohr’s Salt
(B) Nessler’s reagent
(C) Lithium aluminium hydride
(D) Prussian blue coloured complex

Answer 1

Hint: In the above question, we are asked to find out the compound which answers all the tests of its constituent ions. For this, we have to first check if the compound is used for any testing purpose or not then we should check the chemical formula of the compound given along with the information about for determination of which ions, these compounds are used.

Complete step by step solution
Since, in the above question, we are asked to find the compound which answers all tests of constituent ions. So, let us have a brief idea about these compounds.
Mohr’s salt:
In the field of analytical chemistry, Mohr’s salt acts as a source of $ {\text{F}}{{\text{e}}^{{\text{2 + }}}} $ ions . The chemical formula of Mohr’s salt is $ {{\text{(N}}{{\text{H}}_{\text{4}}}{\text{)}}_{\text{2}}}{\text{Fe(S}}{{\text{O}}_{\text{4}}}{{\text{)}}_{\text{2}}}{{\text{(}}{{\text{H}}_{\text{2}}}{\text{O)}}_{\text{6}}} $ . The advantage of using this solid as a source of ferrous ions is that it has a relatively long life and is also resistant to oxidation due to atmospheric exposure. It can answer for all tests of iron and hence, we can say it is used for tests of its constituent ions.
Nessler’s reagent:
Nessler reagent ( $ {{\text{K}}_{\text{2}}}{\text{Hg}}{{\text{I}}_{\text{4}}} $ ) is a solution prepared by combining sodium hydroxide and potassium iodide with mercuric chloride or mercury iodide. When it is reacted with gaseous ammonia, it produces brown fumes or when it is passed through a solution of ammonia, it produces a dirty brown precipitate. It is used for determining the tests of ammonia not for its constituent ions.
Lithium aluminium hydride:
This compound is used as a reducing agent in organic synthesis, especially for the reduction of esters, carboxylic acids and amides. The is dangerously reactive toward water, releasing gaseous hydrogen. It is not used for determining any tests.
Prussian blue coloured complex:
Prussian blue, any of several deep-blue pigments that are composed of complex iron cyanides and hence called iron blues. It is also not used for any kind of testing purpose.
Hence, we can conclude that Mohr’s salt answers all the tests of its constituent ions.
So, the correct option is option A.

Note
Mohr’s salt is sometimes referred to as double salt of ferrous sulfate and ammonium sulfate. It is mainly used in iron plating, photography and in chemical analysis.
Mohr’s salt is quite harmful to the body as it can cause irritation in eyes and skin. High exposure can lead to nausea, stomach pain, diarrhoea and vomiting.