Violet colour appear in glass when we add-

Options

A. `Cr^(3+)`
B. `Mn^(4+)`
C. `I_(2)`
D. `K^(+)`

Explanation

To solve the question regarding the appearance of violet color in glass when certain ions are added, we can follow these steps:

### Step 1: Understand the Context
We need to determine which ion, when added to glass, produces a violet color. The options given are chromium ion (Cr³⁺), manganese ion (Mn⁴⁺), iodine (I₂), and potassium ion (K⁺).

**Hint:** Consider the properties of transition metal ions and their ability to produce colors.

### Step 2: Identify the Ions
Among the options:
- **Cr³⁺ (Chromium ion)**: Known to produce a violet color in glass.
- **Mn⁴⁺ (Manganese ion)**: Typically produces a different color, often yellow or brown.
- **I₂ (Iodine)**: Generally does not impart a violet color.
- **K⁺ (Potassium ion)**: Usually does not contribute to color in glass.

**Hint:** Recall the common colors associated with transition metal ions.

### Step 3: Understand d-d Transitions
Transition metal ions can undergo d-d transitions, where electrons are promoted from one d-orbital to another. The energy difference between these orbitals corresponds to specific wavelengths of visible light, which gives rise to the observed color.

**Hint:** Think about how the color observed is related to the color absorbed.

### Step 4: Determine the Color Produced
When Cr³⁺ is added to glass, it absorbs certain wavelengths of light and reflects/transmits others. The color that is transmitted or reflected is complementary to the color absorbed. In the case of Cr³⁺, it absorbs light in the yellow-green region, resulting in the appearance of violet.

**Hint:** Remember that the observed color is the complementary color of the absorbed light.

### Step 5: Conclusion
Based on the analysis, the correct answer to the question is that violet color appears in glass when chromium ion (Cr³⁺) is added.

**Final Answer:** The violet color appears in glass when we add **Cr³⁺ (Chromium ion)**.