The transition metal ions responsible for colour in ruby and emerald are, respectively :

Options

A. `Cr^(3+) and Cr^(3+)`
B. `Co^(3+) and Co^(3+)`
C. `Co^(3+) and Cr^(3+)`
D. `Cr^(3+) and Co^(3+)`

Answer

To determine the transition metal ions responsible for the color in ruby and emerald, we need to analyze the composition of these gemstones and the role of specific ions in their coloration.

### Step-by-Step Solution:

1. **Identify the Composition of Ruby:**
- Ruby is primarily composed of aluminum oxide (Al₂O₃).
- In ruby, aluminum ions (Al³⁺) are replaced by chromium ions (Cr³⁺).

2. **Understand the Color Mechanism in Ruby:**
- The presence of Cr³⁺ ions in the octahedral sites of the ruby structure leads to color formation.
- The red color of ruby is due to the absorption of certain wavelengths of light, specifically through d-d transitions of the Cr³⁺ ions.

3. **Identify the Composition of Emerald:**
- Emerald is a variety of beryl, with the chemical formula Be₃Al₂(SiO₃)₆.
- Similar to ruby, in emerald, aluminum ions (Al³⁺) are also replaced by chromium ions (Cr³⁺).

4. **Understand the Color Mechanism in Emerald:**
- The green color of emerald is also due to the presence of Cr³⁺ ions.
- The green color results from the absorption of specific wavelengths of light, again through d-d transitions of the Cr³⁺ ions.

5. **Conclusion:**
- Both ruby and emerald derive their colors from the same transition metal ion, which is chromium (Cr³⁺).
- Therefore, the transition metal ions responsible for color in ruby and emerald are, respectively, Cr³⁺ and Cr³⁺.

### Final Answer:
The transition metal ions responsible for color in ruby and emerald are, respectively: **Cr³⁺ and Cr³⁺.**

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