Question

When mercuric iodide is dissolved in KI solution, it shows optical activity. The reason for this behaviour is due to:
A.The common iodide ions
B.The formation of a complex ion
C.Both of them
D.None of them

Answer 1

Hint: Study the reaction of the given reactants. Then carefully study the product formed which is an important reagent.Optical activity is defined as the ability of a chiral molecule to rotate the plane of plane-polarised light. Which is measured using a polarimeter. That is when light passes through a sample that can rotate plane polarised light, the light appears to hazy because it no longer passes straight through the polarising filters.

Complete step by step answer:
Now let’s see how mercuric iodide reacts with KI
When 2 g potassium iodide in 5 ml water is mixed, to this solution, 3 g of mercury (II) iodide is added, and the resulting solution is made to 20 ml, we get a complex as a product $[{K_2}(Hg{I_4})]$. This complex is known as potassium tetraiodomercurate. This is an organic compound consisting of potassium cations and tetraiodomercurate (II) anion.
This compound is very well known as Nessler’s reagent which is a pale-yellow liquid.
This compound is not symmetrical hence shows optical activity.
Hence When mercuric iodide is dissolved in the KI solution, it shows optical activity due to the complex formation. A complex called Nessler's reagent is formed. It is an important reagent in qualitative analysis and is given by the formula $[{K_2}(Hg{I_4})]$ .

So, the correct answer is Option A.

Note: Nessler’s reagent is used to detect ammonia. The pale-yellow solution becomes deep yellow in the presence of ammonia. At higher concentrations, a brown precipitate may form. It is a well known Inorganic reagent widely used for detection of Ammonia. These reactions occur in the basic medium that is the presence of KOH. This reaction is not visible in the water system.