Assertion: Acidified `[Cu(NH_(3))_(4)]^(2+) and [Cu(H_(2)O)_(4)]^(2+)` both react with `K_(4)[Fe(CN)_(6)]` to give brown ppt.
Reason: both complexes are blue in colour of little different shade.

Options

A. If assertion is true but the reason is false
B. If assertion is false but reason is true
C. If both assertion and reason are true and the reason is the correct explanation of assertion
D. If both assertion and reason are true but reason is not the correct explanation of assertion

Answer

To solve the question, we need to analyze both the assertion and the reason provided, and determine their validity as well as the relationship between them.

### Step-by-Step Solution:

1. **Understanding the Assertion**:
- The assertion states that acidified \([Cu(NH_3)_4]^{2+}\) and \([Cu(H_2O)_4]^{2+}\) both react with \(K_4[Fe(CN)_6]\) to give a brown precipitate.
- Copper in both complexes is in the +2 oxidation state (\(Cu^{2+}\)).

2. **Reaction with Potassium Ferrocyanide**:
- When \(Cu^{2+}\) ions react with potassium ferrocyanide \((K_4[Fe(CN)_6])\), they form a complex, specifically \([Cu_2Fe(CN)_6]\), which is known to precipitate as a brown solid.
- Therefore, the assertion is **True**.

3. **Understanding the Reason**:
- The reason states that both complexes are blue in color but of slightly different shades.
- The color of coordination complexes is influenced by the presence of unpaired electrons and the nature of the ligands.
- Both complexes contain \(Cu^{2+}\) which has a \(d^9\) electronic configuration (since \(Cu\) has a configuration of \( [Ar] 4s^1 3d^{10} \) and loses one \(4s\) and one \(3d\) electron to form \(Cu^{2+}\)).

4. **Color Explanation**:
- The color difference arises from the ligand field splitting and the arrangement of unpaired electrons in the \(d\) orbitals.
- \([Cu(H_2O)_4]^{2+}\) and \([Cu(NH_3)_4]^{2+}\) both exhibit different ligand field strengths, leading to slightly different shades of blue.
- Thus, the reason is also **True**.

5. **Evaluating the Relationship**:
- The reason explains the color difference but does not explain why these complexes react with potassium ferrocyanide to form a brown precipitate.
- Therefore, while both statements are true, the reason does not serve as a correct explanation for the assertion.

### Conclusion:
- The assertion is true, the reason is true, but the reason is not the correct explanation for the assertion.

### Final Answer:
Both assertion and reason are true, but the reason is not the correct explanation of the assertion.