Consider the chemical reaction:
`underset(("Green solution"))(Ni^(2+)(aq))+6NH_(3)(aq) hArr underset(("Blue solution"))([Ni(NH_(3))_(6)]^(2+)) (aq)`
When `H^(o+)(aq)` is added, the colour green is favoured. Use one or more of the following interpretations to answer the questions:
i. Some unreacted `Ni^(2+)(aq)` is present in the solution at equilibrium
ii. Some unreacted `NH_(3)(aq)` is present in the solution at equilibrium
iii. The colour change indicates new equilibrium conditions with reduced `[Ni(NH_(3))_(6)]^(2+)(aq)`
iv. The colour change indicates new equilibrium conditions with increased `[Ni(NH_(3))_(6)]^(2+)(aq)`.
The deepening of blue colour on addition of more `NH_(3)(aq)` supports interpretation(s).

Options

A. i only
B. i and iv only
C. i and ii only
D. ii and iv only

Explanation

To solve the problem, we need to analyze the given chemical reaction and the effects of adding `H^+(aq)` and `NH3(aq)` on the equilibrium state of the system.

### Step-by-Step Solution:

1. **Identify the Reaction**:
The reaction is:
\[ \text{Ni}^{2+}(aq) + 6 \text{NH}_3(aq) \rightleftharpoons [\text{Ni(NH}_3)_6]^{2+}(aq) \]
- The left side represents the green solution (Ni²⁺ with NH₃).
- The right side represents the blue solution ([Ni(NH₃)₆]²⁺).

2. **Effect of Adding `H^+(aq)`**:
- When `H^+(aq)` is added, the color green is favored. This indicates that the equilibrium shifts to the left, meaning that the concentration of `Ni²⁺` increases and the concentration of `[Ni(NH₃)₆]²⁺` decreases.

3. **Interpret the Observations**:
- The deepening of the blue color upon adding more `NH₃(aq)` suggests that the equilibrium shifts to the right, favoring the formation of the complex ion `[Ni(NH₃)₆]²⁺`.
- This means that some `NH₃` was unreacted in the solution, allowing the reaction to proceed forward when more `NH₃` is added.

4. **Evaluate the Interpretations**:
- **Interpretation i**: Some unreacted `Ni²⁺` is present in the solution at equilibrium.
- **Evaluation**: Incorrect. At equilibrium, there should be no unreacted species.
- **Interpretation ii**: Some unreacted `NH₃` is present in the solution at equilibrium.
- **Evaluation**: Correct. The deepening blue color indicates that more `NH₃` can react, suggesting some was unreacted.
- **Interpretation iii**: The color change indicates new equilibrium conditions with reduced `[Ni(NH₃)₆]^{2+}`.
- **Evaluation**: Incorrect. The addition of `NH₃` increases the concentration of the complex ion.
- **Interpretation iv**: The color change indicates new equilibrium conditions with increased `[Ni(NH₃)₆]^{2+}`.
- **Evaluation**: Correct. The deepening blue color indicates an increase in the concentration of `[Ni(NH₃)₆]^{2+}`.

5. **Conclusion**:
- The correct interpretations supported by the observations are **ii** and **iv**.