A reagent that can detect any of `Cu^(2+),Fe^(3+),Zn^(2+)` and `Cd^(2+)` is ______(a)______.

Answer

To solve the question of identifying a reagent that can detect any of the ions \( Cu^{2+}, Fe^{3+}, Zn^{2+}, \) and \( Cd^{2+} \), we can follow these steps:

### Step 1: Identify the Ions
We need to recognize the ions we are dealing with:
- Copper ion \( Cu^{2+} \)
- Iron ion \( Fe^{3+} \)
- Zinc ion \( Zn^{2+} \)
- Cadmium ion \( Cd^{2+} \)

### Step 2: Research Reagents
Next, we should consider which reagents are known to react with these ions. One well-known reagent is potassium ferrocyanide \( K_4[Fe(CN)_6] \).

### Step 3: Analyze Reactions
Now, let's analyze how potassium ferrocyanide reacts with each of the ions:
- **For \( Fe^{3+} \)**: It forms a deep blue complex known as Prussian blue, represented by the formula \( Fe_3[Fe(CN)_6] \).
- **For \( Zn^{2+} \)**: It forms a bluish-white precipitate.
- **For \( Cd^{2+} \)**: It also forms a bluish-white precipitate.
- **For \( Cu^{2+} \)**: It produces a reddish-brown precipitate.

### Step 4: Conclusion
Since potassium ferrocyanide can detect all four ions by producing distinct colors or precipitates, we conclude that the reagent that can detect \( Cu^{2+}, Fe^{3+}, Zn^{2+}, \) and \( Cd^{2+} \) is:

**Answer: Potassium Ferrocyanide \( K_4[Fe(CN)_6] \)**

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