`Na_(2)CO_(3)` cannot be used in place of `(NH_(4))_(2)CO_(3)` for the precipitation of group V because

Options

A. `Na^(o+)`interferes in the detection of group V
B. Concentration of `CO_(3)^(2-)` is very low
C. Na will react with acid radicals
D. Mg2+` will be precipitated

Explanation

To understand why sodium carbonate (Na₂CO₃) cannot be used in place of ammonium carbonate ((NH₄)₂CO₃) for the precipitation of group V radicals, we will analyze the properties and behavior of both compounds in solution.

### Step-by-step Solution:

1. **Understanding Group V Radicals**:
Group V in qualitative analysis typically includes ions such as phosphate (PO₄³⁻), arsenate (AsO₄³⁻), and others. The precipitation of these ions is crucial for their identification.

**Hint**: Recall the common ions present in group V for better understanding.

2. **Role of Ammonium Carbonate**:
Ammonium carbonate ((NH₄)₂CO₃) is used for the precipitation of group V radicals because it provides ammonium ions (NH₄⁺) in solution, which do not interfere with the precipitation of group V ions.

**Hint**: Consider how ammonium ions interact with other ions in solution.

3. **Behavior of Sodium Carbonate in Solution**:
When sodium carbonate (Na₂CO₃) is dissolved in water, it dissociates into sodium ions (Na⁺) and carbonate ions (CO₃²⁻). The presence of sodium ions does not contribute to the precipitation of group V ions.

**Hint**: Think about the dissociation of salts in water and the ions produced.

4. **High Concentration of Carbonate Ions**:
Sodium carbonate leads to a higher concentration of carbonate ions (CO₃²⁻) in solution. This increased concentration can exceed the solubility product (Ksp) of not only group V radicals but also magnesium ions (Mg²⁺), causing them to precipitate.

**Hint**: Review the concept of solubility product and how it relates to precipitation.

5. **Precipitation of Magnesium Ions**:
The carbonate ions from sodium carbonate can precipitate magnesium ions (Mg²⁺) as magnesium carbonate (MgCO₃), which is not desirable when trying to identify group V radicals.

**Hint**: Consider the implications of unwanted precipitates in qualitative analysis.

6. **Conclusion**:
Therefore, sodium carbonate cannot be used in place of ammonium carbonate for the precipitation of group V radicals because it leads to the precipitation of magnesium ions and potentially other unwanted ions due to the high concentration of carbonate ions.

**Hint**: Summarize the reasons why one reagent is preferable over the other in qualitative analysis.

### Final Answer:
Sodium carbonate cannot be used in place of ammonium carbonate for the precipitation of group V because it leads to the precipitation of magnesium ions due to the high concentration of carbonate ions, which exceeds the solubility product of both group V radicals and magnesium ions.