`Cr(OH)_(3)+ClO^(-)+3OH^(-)rarr?+Cl^(-)3H_(2)O`. The missing ion is

Options

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

Answer

To solve the question, we need to identify the missing ion in the reaction:

\[ \text{Cr(OH)}_3 + \text{ClO}^- + 3\text{OH}^- \rightarrow ? + \text{Cl}^- + 3\text{H}_2\text{O} \]

### Step-by-Step Solution:

1. **Identify the Reactants:**
- We have chromium hydroxide, \(\text{Cr(OH)}_3\), which contains chromium in the +3 oxidation state.
- We also have hypochlorite ion, \(\text{ClO}^-\), and hydroxide ions, \(\text{OH}^-\).

2. **Determine the Products:**
- The products include chloride ion, \(\text{Cl}^-\), and water, \(3\text{H}_2\text{O}\).
- We need to find the missing product.

3. **Oxidation State Changes:**
- In \(\text{Cr(OH)}_3\), chromium has an oxidation state of +3.
- In the potential product, \(\text{CrO}_4^{2-}\) (chromate ion), chromium has an oxidation state of +6.
- This indicates that chromium is being oxidized from +3 to +6.

4. **Oxidizing Agent:**
- The hypochlorite ion, \(\text{ClO}^-\), acts as an oxidizing agent in this reaction, facilitating the oxidation of chromium.

5. **Balancing the Reaction:**
- The hypochlorite ion oxidizes chromium hydroxide to chromate ion, \(\text{CrO}_4^{2-}\).
- Therefore, the missing ion in the reaction is \(\text{CrO}_4^{2-}\).

6. **Final Reaction:**
- The balanced reaction can be written as:
\[ \text{Cr(OH)}_3 + \text{ClO}^- + 3\text{OH}^- \rightarrow \text{CrO}_4^{2-} + \text{Cl}^- + 3\text{H}_2\text{O} \]

### Conclusion:
The missing ion in the reaction is \(\text{CrO}_4^{2-}\) (chromate ion).