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 arrange the given compounds in order of decreasing acidity, we need to analyze the effects of the nitro groups (-NO2) on the acidity of the compounds. The presence of electron-withdrawing groups like -NO2 increases acidity by stabilizing the negative charge on the conjugate base formed after deprotonation.

### Step-by-Step Solution:

1. **Identify the Compounds:**
- 1. `CH3-NO2` (Nitromethane)
- 2. `NO2-CH2-NO2` (1,2-Dinitroethane)
- 3. `CH3-CH2-NO2` (Ethyl nitrite)
- 4. `NO2-CH(NO2)-NO2` (1,3-Dinitro-2-propanol)

2. **Assess the Acidity:**
- **Compound 1: `CH3-NO2`**: This compound has one nitro group which can stabilize the negative charge after deprotonation.
- **Compound 2: `NO2-CH2-NO2`**: This compound has two nitro groups, which significantly increases its acidity due to greater stabilization of the conjugate base.
- **Compound 3: `CH3-CH2-NO2`**: This compound has one nitro group but is less acidic than `CH3-NO2` because the ethyl group is less electron-withdrawing than the methyl group.
- **Compound 4: `NO2-CH(NO2)-NO2`**: This compound has three nitro groups, making it the most acidic due to maximum stabilization of the conjugate base.

3. **Rank the Compounds:**
- The compound with the most nitro groups will be the most acidic.
- Therefore, the order of decreasing acidity is:
- 4. `NO2-CH(NO2)-NO2` (most acidic)
- 2. `NO2-CH2-NO2`
- 1. `CH3-NO2`
- 3. `CH3-CH2-NO2` (least acidic)

### Final Order of Acidity:
4 > 2 > 1 > 3