Quantitative estimatin of `C,H` and extra elements (e.g., N.S.P., and halogens) is carried out by Liebig's combustion, Carius, Dumas, and Kjeldahl's method.
Q. In carius method for the quantitative estimation of phosphorous by using magnesia mixture, phosphorous is estimated by:

Options

A. `MgNH_4PO_4`
B. `Mg_2P_2O_7`
C. `(NH_4)_3PO_4.12MoO_3`
D. All

Answer

To solve the question regarding the quantitative estimation of phosphorus using the Carius method with a magnesia mixture, we can break it down into the following steps:

### Step-by-Step Solution:

1. **Understanding the Carius Method**:
The Carius method is a technique used for the quantitative estimation of phosphorus in organic compounds. It involves the oxidation of phosphorus to phosphoric acid.

**Hint**: Remember that the Carius method specifically involves oxidation reactions.

2. **Oxidation of Phosphorus**:
In this method, the organic compound containing phosphorus is treated with fuming nitric acid (HNO3). The fuming nitric acid acts as an oxidizing agent and converts all the phosphorus present in the compound into phosphoric acid (H3PO4).

**Hint**: Identify the role of fuming nitric acid in the oxidation process.

3. **Formation of Phosphoric Acid**:
The reaction with fuming nitric acid results in the formation of phosphoric acid, which is crucial for the subsequent steps.

**Hint**: Phosphoric acid is the key product formed from the oxidation of phosphorus.

4. **Treatment with Magnesia Mixture**:
The phosphoric acid obtained is then treated with a magnesia mixture. The magnesia mixture consists of magnesium chloride (MgCl2), ammonium chloride (NH4Cl), and ammonia (NH3).

**Hint**: Know the components of the magnesia mixture and their roles.

5. **Precipitation of Magnesium Ammonium Phosphate**:
Upon treatment with the magnesia mixture, a precipitate of magnesium ammonium phosphate (MgNH4PO4) is formed.

**Hint**: This step involves the formation of a solid precipitate from the solution.

6. **Ignition of the Precipitate**:
The precipitate of magnesium ammonium phosphate is then ignited. Upon ignition, it decomposes to form magnesium pyrophosphate (Mg2P2O7).

**Hint**: The ignition process transforms the precipitate into a different compound.

7. **Weighing and Calculation**:
The magnesium pyrophosphate is dried and weighed. The percentage of phosphorus in the original compound can be calculated using the formula:

\[ \text{Percentage of Phosphorus} = \left( \frac{62}{222} \times \frac{W_{Mg2P2O7}}{W_{compound}} \right) \times 100 \]

where \( W_{Mg2P2O7} \) is the weight of the magnesium pyrophosphate and \( W_{compound} \) is the weight of the original compound.

**Hint**: Familiarize yourself with the formula for calculating the percentage of phosphorus.

### Final Answer:
In the Carius method for the quantitative estimation of phosphorus using a magnesia mixture, phosphorus is estimated by the formation of **magnesium pyrophosphate (Mg2P2O7)**.