In the following question, a statement of assertion is followed by a statement of reason . Mark the correct choice.
Assertion : ` [Cu(NH_(3))_(4)]^(2+)` is coloured while ` [Cu(CN)_(4)]^(3-)` is colourless .
Reason : ` [Cu(NH_(3))_(4)]^(2+)` has ` dsp^(2)` hydridisation

Options

A. Both assertion and reason are true and reason is the correct explanation of assertion .
B. Both assertion and reason are true but reason . Is not the correct explanation of assertion.
C. Assertion is true but reason is false.
D. Both assertion and reason are false.

Answer

To solve the question, we will analyze both the assertion and the reason provided.

### Step-by-Step Solution:

1. **Understanding the Assertion**:
- The assertion states that `[Cu(NH₃)₄]²⁺` is colored while `[Cu(CN)₄]³⁻` is colorless.
- To evaluate this, we need to consider the oxidation states and electronic configurations of copper in both complexes.

2. **Analyzing `[Cu(NH₃)₄]²⁺`**:
- Ammonia (NH₃) is a neutral ligand, so the oxidation state of copper in this complex is +2.
- The electron configuration of copper is [Ar] 3d¹⁰ 4s¹. For Cu²⁺, it becomes 3d⁹ (since it loses two electrons).
- In the 3d⁹ configuration, there is one unpaired electron, which allows for d-d transitions when light is absorbed, resulting in a colored complex.

3. **Analyzing `[Cu(CN)₄]³⁻`**:
- Cyanide (CN⁻) is a strong field ligand, and here, the oxidation state of copper is +1 (since CN⁻ has a -1 charge and the overall charge is -3).
- The electron configuration for Cu⁺ is 3d¹⁰ (it loses one 4s electron).
- With a fully filled 3d¹⁰ configuration, there are no unpaired electrons, meaning there are no d-d transitions possible. Thus, this complex is colorless.

4. **Understanding the Reason**:
- The reason states that `[Cu(NH₃)₄]²⁺` has dsp² hybridization.
- However, for `[Cu(NH₃)₄]²⁺`, the hybridization is actually sp³ due to the four ammonia ligands forming a tetrahedral arrangement around the copper ion.

5. **Conclusion**:
- The assertion is true: `[Cu(NH₃)₄]²⁺` is colored and `[Cu(CN)₄]³⁻` is colorless.
- The reason is false because the hybridization of `[Cu(NH₃)₄]²⁺` is not dsp² but rather sp³.

### Final Answer:
- The correct choice is that the assertion is true, but the reason is false.