In qualitative inorganic analysis phosphate , if present, is to be eliminated in the appropriate group in order to detect the radical :

Options

A. `Pb^(2+)`
B. `As^(3+)`
C. `Ca^(2+)`
D. `Cd^(2+)`

Explanation

To solve the problem of eliminating phosphate (PO4^3-) in qualitative inorganic analysis to detect specific cations, we can follow these steps:

### Step-by-Step Solution:

1. **Identify the Groups of Cations**:
- In qualitative analysis, cations are divided into groups based on their solubility and precipitation reactions.
- Lead (Pb^2+), Arsenic (As^2+), and Cadmium (Cd^2+) belong to Group 2, while Calcium (Ca^2+) belongs to Group 5.

2. **Understand the Role of Phosphate**:
- Phosphate ions (PO4^3-) can form insoluble salts with certain cations. This can interfere with the detection of these cations in qualitative analysis.

3. **Determine the Interference**:
- Since Pb^2+, As^2+, and Cd^2+ are in Group 2, the presence of phosphate will not interfere with their detection.
- However, since Ca^2+ is in Group 5, phosphate can form insoluble calcium phosphate (Ca3(PO4)2), which will interfere with the detection of calcium ions.

4. **Eliminate Phosphate for Detection**:
- To accurately detect Ca^2+, we need to eliminate the phosphate ions from the solution. This can be done by adding a reagent that precipitates phosphate as an insoluble compound or by adjusting the pH to prevent phosphate from interfering.

5. **Conclusion**:
- The cation that requires the elimination of phosphate for better detection is Calcium (Ca^2+). Therefore, the answer to the question is Calcium (Ca^2+).

### Final Answer:
The radical that requires the elimination of phosphate for better detection is **Calcium (Ca^2+)**.

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