"A" obtained by Ostwald's method involving air oxidation of NH3, upon further air oxidation produces "B". "B" on hydration forms an oxoacid of Nitrogen along with evolution of "A". The oxyacid also produces "A" gives positive brown ring test.
Identify and A and B, respectively

Options

A. `NO,NO_(2)`
B. `NO_(2),N_(2)O_(4)`
C. `N_(2)O_(3),NO_(2)`
D. `NO_(2),N_(2)O_(5)`

Answer

To solve the problem, we need to identify the compounds "A" and "B" based on the given information about their formation and reactions.

### Step-by-Step Solution:

1. **Identify "A" from Ostwald's Method**:
- Ostwald's method involves the oxidation of ammonia (NH3) in the presence of air (oxygen). The primary product of this reaction is nitrogen monoxide (NO).
- Therefore, we can conclude that **A = NO**.

2. **Determine "B" from the Further Oxidation of "A"**:
- The question states that "A" (which we identified as NO) undergoes further air oxidation. When nitrogen monoxide (NO) is oxidized by oxygen (O2), it forms nitrogen dioxide (NO2).
- Thus, we have **B = NO2**.

3. **Hydration of "B" to Form an Oxoacid**:
- The next part of the question mentions that "B" (NO2) upon hydration forms an oxoacid of nitrogen. When NO2 is dissolved in water, it forms nitric acid (HNO3).
- Therefore, the oxoacid formed is **HNO3**.

4. **Evolution of "A" from the Oxoacid**:
- The question also states that this oxoacid (HNO3) evolves "A" (NO) upon some reaction. This can occur in certain conditions where nitric acid can decompose to release nitrogen monoxide.
- Thus, we confirm that **A = NO** and **B = NO2**.

5. **Brown Ring Test**:
- Finally, the oxoacid (HNO3) is known to give a positive brown ring test when reacted with ferrous sulfate (FeSO4) in the presence of sulfuric acid (H2SO4), confirming the presence of nitrate ions (NO3^-).
- This aligns with our findings that HNO3 can produce NO.

### Conclusion:
- Therefore, the correct identification of the compounds is:
- **A = NO**
- **B = NO2**