When excess of dilute `NH_(4)OH` is added to an aqueous solution of copper sulphate an intense blue colour is developed.This is due to the formation of:

Options

A. `[Cu(NH_(3))_(6)]^(2+)`
B. `Cu(OH)_(2)`
C. `[Cu(NH_(3))_(4)]^(2+)`
D. `(NH_(4))_(2)SO_(4)`

Answer

To solve the question regarding the formation of an intense blue color when excess dilute NH₄OH is added to an aqueous solution of copper sulfate (CuSO₄), we can follow these steps:

### Step-by-Step Solution:

1. **Identify the Reactants**: The reactants in this scenario are copper sulfate (CuSO₄) and dilute ammonium hydroxide (NH₄OH).

2. **Understand the Reaction**: When NH₄OH is added to CuSO₄, it reacts with the copper ions (Cu²⁺) present in the solution.

3. **Determine the Role of Excess NH₄OH**: Since NH₄OH is in excess, it will facilitate the formation of a complex ion rather than just a simple precipitation reaction.

4. **Formation of the Complex**: The excess NH₄OH will lead to the formation of the complex ion [Cu(NH₃)₄]²⁺. This complex is known as tetraamminecopper(II) ion.

5. **Color of the Complex**: The complex ion [Cu(NH₃)₄]²⁺ is known to exhibit an intense blue color, which is characteristic of copper(II) complexes with ammonia.

6. **Conclusion**: Therefore, the intense blue color observed in the solution is due to the formation of the complex [Cu(NH₃)₄]²⁺.

### Final Answer:
The intense blue color developed when excess dilute NH₄OH is added to an aqueous solution of copper sulfate is due to the formation of the complex ion [Cu(NH₃)₄]²⁺.