`Cu^(+)` ions reacts with `Fe^(+)` ion according to the following reaction `Cu^(+) + 2Fe^(2+)hArrCu+2Fe^(3+)` At equilibrium the concentration of `Cu^(2+)` ions is not changed by the addition of

Options

A. `Cu^(2+)`
B. `Fe^(2+)`
C. `Cu`
D. `Fe^(3+)`

Answer

To solve the question regarding the reaction between `Cu^(+)` ions and `Fe^(2+)` ions, we need to analyze the equilibrium expression and understand how the addition of different substances affects the concentration of `Cu^(2+)` ions.

### Step-by-Step Solution:

1. **Write the Reaction**:
The reaction given is:
\[ Cu^{+} + 2Fe^{2+} \rightleftharpoons Cu^{2+} + 2Fe^{3+} \]

2. **Identify the Equilibrium Expression**:
The equilibrium constant expression \( K_c \) for the reaction is formulated based on the concentrations of the products and reactants:
\[ K_c = \frac{[Cu^{2+}][Fe^{3+}]^2}{[Cu^{+}][Fe^{2+}]^2} \]
Here, only the concentrations of the aqueous ions are included in the expression. Solids and pure liquids do not appear in the equilibrium constant expression.

3. **Determine What Affects the Concentration of `Cu^{2+}`**:
The question asks what addition does not change the concentration of `Cu^{2+}` ions. Since `Cu^{2+}` is part of the equilibrium expression, any change in the concentrations of the reactants or products that are included in the expression will affect the equilibrium position.

4. **Consider the Addition of Different Substances**:
- If we add more `Cu` (solid), it does not affect the equilibrium since it is not included in the equilibrium expression.
- If we add more `Fe^{2+}` or `Cu^{2+}`, it will shift the equilibrium according to Le Chatelier's principle, affecting the concentration of `Cu^{2+}`.
- Adding `Fe^{3+}` will also affect the equilibrium since it is part of the expression.

5. **Conclusion**:
The only addition that does not change the concentration of `Cu^{2+}` ions is the addition of solid `Cu` because it does not appear in the equilibrium expression.

### Final Answer:
The concentration of `Cu^{2+}` ions is not changed by the addition of **solid `Cu`**.