In Nessler's reagent, the ion present is

Options

A. `HgI^(2-)`
B. `HgI_(4)^(2-)`
C. `Hg^(+)`
D. `Hg^(2)`

Answer

To solve the question regarding the ion present in Nessler's reagent, we can follow these steps:

### Step 1: Understand what Nessler's reagent is
Nessler's reagent is a chemical solution used primarily for detecting ammonia. It is formed by the combination of mercuric iodide (HgI2) with potassium iodide (KI) and potassium hydroxide (KOH).

**Hint:** Research the components that make up Nessler's reagent and their roles in the formation of the reagent.

### Step 2: Identify the chemical composition of Nessler's reagent
When mercuric iodide (HgI2) is mixed with potassium iodide (KI) and potassium hydroxide (KOH), it results in the formation of a complex ion. The key product of this reaction is the alkaline solution of potassium tetraiodomercurate(II), which can be represented as K2HgI4.

**Hint:** Look for the chemical reaction that occurs when these components are mixed to understand the resulting compound.

### Step 3: Determine the active ion in Nessler's reagent
The active ion in Nessler's reagent is the tetraiodomercurate ion, which is represented as HgI4^2-. This ion is responsible for the characteristic color change observed when ammonia is present in the solution.

**Hint:** Focus on the structure of the complex ion formed and its charge to identify the active species.

### Step 4: Compare with the given options
The question provides several options: HgI2-, HgI4-, Hg+, and Hg2+. Among these, the correct answer is HgI4^2-, as it is the active ion present in Nessler's reagent.

**Hint:** Eliminate the incorrect options by analyzing their chemical formulas and charges to find the one that matches the identified active ion.

### Final Answer
The ion present in Nessler's reagent is **HgI4^2-**.