The ion which exhibits orange red colour in aqueous solution is

Options

A. `Cr_(2)O_(7)^(2-)`
B. `MnO_(4)^(2-)`
C. `MnO_(4)^(-)`
D. `Cr^(3+)`

Answer

To determine which ion exhibits an orange-red color in aqueous solution, we will analyze the given options step by step.

### Step 1: Identify the given ions
The options provided are:
1. \( \text{Cr}_2\text{O}_7^{2-} \) (Dichromate ion)
2. \( \text{MnO}_4^{-} \) (Permanganate ion)
3. \( \text{MnO}_2^{2-} \) (Manganese dioxide ion)
4. \( \text{Cr}^{3+} \) (Chromium ion)

### Step 2: Analyze the color of each ion
- **Dichromate ion (\( \text{Cr}_2\text{O}_7^{2-} \))**: This ion is known to exhibit an orange-red color in aqueous solution due to the presence of unpaired electrons and d-d transitions.

- **Permanganate ion (\( \text{MnO}_4^{-} \))**: This ion typically exhibits a deep purple color in solution, not orange-red.

- **Manganese dioxide ion (\( \text{MnO}_2^{2-} \))**: This ion does not have a distinct color in aqueous solution and is generally considered to be colorless.

- **Chromium ion (\( \text{Cr}^{3+} \))**: This ion usually appears green in solution.

### Step 3: Conclusion
Based on the analysis above, the ion that exhibits an orange-red color in aqueous solution is the **dichromate ion (\( \text{Cr}_2\text{O}_7^{2-} \))**.

### Final Answer:
The ion which exhibits orange-red color in aqueous solution is \( \text{Cr}_2\text{O}_7^{2-} \).

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