White compound `Aoverset(HNO_3)toBoverset(I_2)to` C(used to estimate CO). The compound A is

Options

A. `P_2O_5`
B. `I_2O_5`
C. `I_4O_9`
D. `S_3O_9`

Answer

To solve the question regarding the white compound A, let's break it down step by step:

### Step 1: Identify Compound A
The question states that compound A is a white compound that reacts with HNO3 (Nitric Acid) to form compound B. Based on common chemical knowledge, a well-known white compound that fits this description is Phosphorus Pentoxide (P2O5).

### Step 2: Reaction of Compound A with HNO3
When Phosphorus Pentoxide (P2O5) reacts with Nitric Acid (HNO3), it forms Dinitrogen Pentoxide (N2O5) and water. The balanced reaction can be represented as:
\[ P_2O_5 + 4 HNO_3 \rightarrow 2 N_2O_5 + 2 H_2O \]
Thus, compound B is Dinitrogen Pentoxide (N2O5).

### Step 3: Reaction of Compound B with I2
Next, the question indicates that compound B (N2O5) reacts with Iodine (I2) to form compound C. The reaction can be represented as:
\[ N_2O_5 + I_2 \rightarrow I_2O_5 + N_2 \]
Here, compound C is Iodine Pentoxide (I2O5).

### Step 4: Use of Compound C
The question mentions that compound C (I2O5) is used to estimate Carbon Monoxide (CO). In the presence of air, Iodine Pentoxide reacts with Carbon Monoxide to produce Carbon Dioxide (CO2) and solid Iodide. The reaction can be summarized as:
\[ I_2O_5 + CO \rightarrow CO_2 + I_2 \]
This confirms that I2O5 is indeed used for estimating CO.

### Conclusion
Thus, the white compound A is Phosphorus Pentoxide (P2O5).

### Final Answer
The compound A is Phosphorus Pentoxide (P2O5).

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