Arrange given compounds in order of decreasing acidity
1. `CH_3-NO_2`
2. `NO_2-CH_2-NO_2`
3. `CH_3-CH_2-NO_2`
4. `NO_2-underset(NO_2)underset(|)(CH)-NO_2`

Options

A. `4 gt 2 gt 1 gt 3`
B. `4 gt 2 gt 3 gt 1`
C. `3gt 1 gt 2 gt 4`
D. `3 gt 1 gt 4 gt 2`

Answer

To determine the order of decreasing acidity of the given compounds, we need to analyze the effect of the nitro (NO2) groups on the acidity of each compound. The acidity of a compound is influenced by the ability of the compound to lose a proton (H⁺ ion). The presence of electron-withdrawing groups, such as nitro groups, increases acidity by stabilizing the negative charge that results from losing a proton.

### Step-by-Step Solution:

1. **Identify the Compounds**:
- 1. `CH₃-NO₂`
- 2. `NO₂-CH₂-NO₂`
- 3. `CH₃-CH₂-NO₂`
- 4. `NO₂-CH-NO₂`

2. **Analyze the Effect of Nitro Groups**:
- Nitro groups (NO₂) are strong electron-withdrawing groups. The more nitro groups attached to a compound, the more acidic it becomes because they stabilize the negative charge that forms when a proton is lost.

3. **Count the Nitro Groups**:
- Compound 1 (`CH₃-NO₂`): 1 nitro group
- Compound 2 (`NO₂-CH₂-NO₂`): 2 nitro groups
- Compound 3 (`CH₃-CH₂-NO₂`): 1 nitro group
- Compound 4 (`NO₂-CH-NO₂`): 2 nitro groups

4. **Determine the Acidity Order**:
- Compound 4 has 2 nitro groups and is likely the most acidic.
- Compound 2 also has 2 nitro groups, but they are positioned differently, which can affect acidity slightly. However, it will still be very acidic.
- Compounds 1 and 3 both have 1 nitro group, but compound 3 has an additional alkyl group (ethyl) that can donate electron density, making it less acidic than compound 1.

5. **Final Order of Acidity**:
- The order of decreasing acidity is:
- 4 (`NO₂-CH-NO₂`) > 2 (`NO₂-CH₂-NO₂`) > 1 (`CH₃-NO₂`) > 3 (`CH₃-CH₂-NO₂`)

### Conclusion:
The final order of decreasing acidity for the compounds is:
- **4 > 2 > 1 > 3**