Which reagent can be used to identify `Ni^(2+)` ion ?

Options

A. Resorcinol
B. Dimethyl glyoxime
C. Diphenyl benzidine
D. Potassium ferrocyanide

Answer

To identify the `Ni^(2+)` ion, we can use the following steps:

### Step-by-Step Solution:

1. **Understanding the Question**: We need to identify which reagent can be used to detect the presence of nickel ions (`Ni^(2+)`).

2. **Reviewing the Options**: The options provided are:
- Option 1: Resorcinol
- Option 2: Dimethylglyoxane (DMG)
- Option 3: Diphenylbenzidine
- Option 4: Potassium ferrocyanide

3. **Identifying the Correct Reagent**:
- Among the options, **Dimethylglyoxane (DMG)** is known to react with nickel ions.
- When nickel salts (like NiCl2) react with dimethylglyoxane in the presence of ammonium hydroxide (NH4OH), they form a scarlet red precipitate of nickel dimethylglyoxane.

4. **Chemical Reaction**: The reaction can be summarized as follows:
- **Reactants**: NiCl2 + 2 DMG + 2 NH4OH
- **Products**: Nickel dimethylglyoxane (scarlet red precipitate) + 2 NH4Cl + Water

5. **Conclusion**: Based on the reaction, we conclude that the reagent used to identify `Ni^(2+)` ion is **Dimethylglyoxane (DMG)**. Therefore, the correct answer is **Option 2**.