Which of the following does not give borax bead test ?

Options

A. `Cr^(3+)`
B. `Co^(2+)`
C. `Ag^(+)`
D. `Zn^(2+)`

Answer

To solve the question "Which of the following does not give borax bead test?" we will analyze the given options: Cr³⁺, Co²⁺, Ag⁺, and Zn²⁺.

### Step-by-Step Solution:

1. **Understanding the Borax Bead Test:**
- The borax bead test is a qualitative analysis method used to identify certain metal ions based on the color of the bead formed when the metal salt is heated with borax.
- A platinum wire loop is dipped into borax and heated to form a bead. This bead is then dipped into the salt of the metal ion and heated again. The resulting color of the bead helps identify the metal ion.

2. **Identifying the Metal Ions:**
- **Cr³⁺ (Chromium ion):** This ion typically gives a green color when subjected to the borax bead test.
- **Co²⁺ (Cobalt ion):** This ion produces a blue color in the borax bead test.
- **Ag⁺ (Silver ion):** Silver ions can give a yellow color when tested with borax.
- **Zn²⁺ (Zinc ion):** Zinc ions do not produce any color in the borax bead test.

3. **Analyzing the Color of Salts:**
- The key point to remember is that the borax bead test is effective for colored metal ions.
- Cr³⁺, Co²⁺, and Ag⁺ all form colored salts, which can be identified through the borax bead test.
- Zn²⁺, on the other hand, forms colorless salts because it has a fully filled d-orbital (3D¹⁰), which means it does not have any unpaired electrons to contribute to color.

4. **Conclusion:**
- Since Zn²⁺ does not produce a color in the borax bead test, it is the ion that does not give a positive result in this test.

Thus, the answer is **Zn²⁺**.

### Final Answer:
**Zn²⁺ does not give the borax bead test.**

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