Question

The metal ion whose electronic configuration is not affected by the nature of the ligand and which gives a violet color in non-luminous flame under hot condition in borax bead test is:

• A. Ti$^{3+}$
• B. Mn$^{2+}$
• C. Cr$^{3+}$
• D. Ni$^{2+}$

Hint:

The borax bead test is useful for detecting certain metal ions in compounds due to characteristic colors they produce when heated in borax.

Answer 1

The Correct Option is B

The borax bead test is a qualitative chemical test used to detect the presence of certain metal ions. It works by reacting metal salts with borax $ Na_2B_4O_7 \cdot 10H_2O $, which on heating forms a glassy bead containing metal borates. The color of the bead is characteristic of the metal ion present.

Hot bead colors for the following transition metal ions:

1. Cr³⁺: Green when hot, blue-green when cold
2. Mn²⁺: Violet
3. Ni²⁺: Reddish brown

Manganese(II) ions (Mn²⁺) produce a violet-colored bead in the borax bead test. Additionally, Mn²⁺ has a d⁵ electronic configuration, which is relatively stable and less influenced by the surrounding ligand field, making it a distinctive case.

Electronic configurations:

• $ Ti^{3+} $: d¹
• $ Ni^{2+} $: d⁸
• $ Mn^{2+} $: d⁵
• $ Cr^{3+} $: d³

Among the given options, $ Mn^{2+} $ matches both the observed color and the electronic configuration.

Final Answer:
The final answer is $ Mn^{2+} $.

Answer 2

Step 1: Understand the question.
We need to find the metal ion whose electronic configuration does not change with the nature of the ligand and that produces a violet color in the borax bead test when heated in a non-luminous flame.

Step 2: Recall the borax bead test principle.
In this test, a small borax bead is heated with a metal salt. The metal ion forms a colored metaborate, and the resulting color helps identify the ion. The color observed depends on the oxidation state and the electronic configuration of the ion.

Step 3: Analyze the ligand effect and stability of configuration.
A metal ion whose electronic configuration is unaffected by the ligand field must have either a half-filled or fully filled d-subshell. Such ions are relatively stable and show minimal crystal field splitting.
For Mn²⁺, the electronic configuration is [Ar] 3d⁵, which is half-filled and therefore very stable. This configuration remains the same irrespective of the nature of the ligand.

Step 4: Identify the color in the borax bead test.
In the borax bead test:
- Mn²⁺ gives an amethyst or violet-colored bead in the hot condition.
- Upon cooling, this color becomes lighter or faint pink.

Step 5: Conclusion.
Hence, the metal ion that satisfies both conditions — unchanged electronic configuration and violet color in the hot borax bead test — is Mn²⁺.

Final Answer:
Mn²⁺