Nessler's reagent is used to detect `NH_(3)` this reagentis prepared by mixing

Options

A. `Kl` (excess) `+HgCl_(2)+KOH`
B. `KCl+Hgl_(2)+KOH`
C. `Kl` (excess) `+HgCl_(2)+NH_(4)^(+)OH^(-)`
D. `Kl` (excess) `+Hg_(2)Cl_(2)+l_(2)` solution.

Explanation

To prepare Nessler's reagent, we need to follow a series of steps involving the mixing of specific chemicals. Here’s a step-by-step solution to the question:

### Step 1: Identify the Components
Nessler's reagent is primarily a complex formed from mercury and iodide ions. The key components for its preparation are potassium iodide (KI), mercury(II) chloride (HgCl2), and potassium hydroxide (KOH).

### Step 2: Initial Reaction
First, we mix potassium iodide (KI) with mercury(II) chloride (HgCl2). This reaction produces potassium chloride (KCl) and mercury(II) iodide (HgI2):
\[ 2 \text{KI} + \text{HgCl}_2 \rightarrow 2 \text{KCl} + \text{HgI}_2 \]

### Step 3: Formation of the Complex
Next, we treat the mercury(II) iodide (HgI2) with an excess of potassium iodide (KI). This results in the formation of the complex potassium tetraiodomercurate(II) (K2HgI4):
\[ \text{HgI}_2 + 2 \text{KI} \rightarrow \text{K}_2\text{HgI}_4 \]

### Step 4: Final Preparation of Nessler's Reagent
Finally, we mix the complex K2HgI4 with potassium hydroxide (KOH) to prepare Nessler's reagent:
\[ \text{K}_2\text{HgI}_4 + 2 \text{KOH} \rightarrow \text{Nessler's Reagent} \]

### Conclusion
Thus, Nessler's reagent is prepared by mixing potassium iodide (KI) with mercury(II) chloride (HgCl2) and potassium hydroxide (KOH).

### Answer:
Nessler's reagent is prepared by mixing potassium iodide (KI), mercury(II) chloride (HgCl2), and potassium hydroxide (KOH).

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