Which of the following statement is not true for the reaction given below:
`[Cu(H_(2)O)_(4)]^(2+)+ 4NH_(4) hArr [Cu(NH_(3))_(4)]^(2+)+4H_(2)O`

Options

A. It is ligand substitution reaction
B. `NH_(3)` is a relatively strong field ligand while `H_(2)O` is a weak field ligand
C. During the reaction, there is a change in colour from light blue to dark blue
D. `[Cu(NH_(3))_(4)]^(2+)`, has a tetrahedral structure and is paramagnetic

Explanation

To determine which statement is not true for the given reaction:

\[ [Cu(H_2O)_4]^{2+} + 4NH_3 \rightleftharpoons [Cu(NH_3)_4]^{2+} + 4H_2O \]

we will analyze each part of the reaction and the associated statements.

### Step 1: Identify the type of reaction
This reaction is a ligand substitution reaction where water (a weaker field ligand) is replaced by ammonia (a stronger field ligand).

**Hint:** Look for the type of ligands involved in the reaction and their relative strengths.

### Step 2: Analyze the ligands
Ammonia (NH₃) is indeed a stronger field ligand compared to water (H₂O). This is consistent with the spectrochemical series, where ligands are ranked based on their ability to split the d-orbitals.

**Hint:** Refer to the spectrochemical series to compare the strength of ligands.

### Step 3: Check the color change
The reaction shows a color change from light blue (for the tetrahedral [Cu(H₂O)₄]²⁺ complex) to dark blue (for the square planar [Cu(NH₃)₄]²⁺ complex). This color change is typical when transitioning from a weaker field ligand to a stronger field ligand.

**Hint:** Consider the colors associated with different coordination complexes of copper.

### Step 4: Determine the geometry of the complexes
The geometry of the [Cu(NH₃)₄]²⁺ complex is square planar due to dsp² hybridization, which occurs when copper is in the +2 oxidation state. The statement claiming that the complex has a tetrahedral structure is incorrect.

**Hint:** Recall the hybridization and geometry associated with transition metal complexes and their oxidation states.

### Step 5: Assess paramagnetism
The [Cu(NH₃)₄]²⁺ complex is paramagnetic because it has one unpaired electron in the d-orbitals. This is consistent with the presence of unpaired electrons in the copper complex.

**Hint:** Check the electron configuration and count the number of unpaired electrons to determine paramagnetism.

### Conclusion
The statement that is not true is that the complex has a tetrahedral structure. The correct geometry is square planar due to dsp² hybridization.

### Final Answer
The statement that is not true for the reaction is: "The complex has a tetrahedral structure."