KI solution is the reagent for :

Options

A. `Hg^(2+)`
B. `Pb^(2+)`
C. `Ag^(+)`
D. `Cu^(2+)`

Explanation

To determine the reagents for which KI (potassium iodide) solution acts as a reagent, we need to analyze its reactions with specific metal ions. Here’s a step-by-step breakdown of the reactions:

### Step 1: Identify the metal ions that react with KI
KI solution is known to react with several metal ions, including:
- Mercury (Hg²⁺)
- Lead (Pb²⁺)
- Silver (Ag⁺)
- Copper (Cu²⁺)

### Step 2: Reaction with Mercury (Hg²⁺)
When KI solution reacts with mercury(II) ions (Hg²⁺), it forms mercury(I) iodide (HgI₂):
\[ \text{Hg}^{2+} + 2 \text{KI} \rightarrow \text{HgI}_2 + 2 \text{K}^+ \]
- **Observation**: The product, HgI₂, appears as an orange precipitate.

### Step 3: Reaction with Lead (Pb²⁺)
When KI solution reacts with lead(II) ions (Pb²⁺), it forms lead(II) iodide (PbI₂):
\[ \text{Pb}^{2+} + 2 \text{KI} \rightarrow \text{PbI}_2 + 2 \text{K}^+ \]
- **Observation**: The product, PbI₂, appears as a bright yellow precipitate.

### Step 4: Reaction with Silver (Ag⁺)
When KI solution reacts with silver ions (Ag⁺), it forms silver iodide (AgI):
\[ \text{Ag}^{+} + \text{KI} \rightarrow \text{AgI} + \text{K}^{+} \]
- **Observation**: The product, AgI, also appears as a yellow precipitate.

### Step 5: Reaction with Copper (Cu²⁺)
When KI solution reacts with copper(II) ions (Cu²⁺), it forms copper(I) iodide (CuI):
\[ \text{Cu}^{2+} + 2 \text{KI} \rightarrow \text{CuI}_2 + 2 \text{K}^+ \]
- **Observation**: The product, CuI, is typically a white precipitate.

### Conclusion
KI solution acts as a reagent for the following metal ions:
- **Hg²⁺**: Forms orange HgI₂
- **Pb²⁺**: Forms bright yellow PbI₂
- **Ag⁺**: Forms yellow AgI
- **Cu²⁺**: Forms white CuI