The decreasing order of -I effect of the following is
I. `-overset(o+)NH_(3)`.
II. `-NO_(2)`
III. `-CN`
IV. `-COOH`

Options

A. I gt II gt III gt IV
B. II gt I gt III gt IV
C. I gt II gt III gt IV
D. II gt I gt IV gt III

Answer

To determine the decreasing order of the -I (negative inductive) effect of the given groups, we need to analyze the electron-withdrawing ability of each group. The -I effect refers to the ability of a substituent to pull electron density away from the rest of the molecule, which is typically due to electronegativity or the presence of multiple bonds.

### Step-by-Step Solution:

1. **Identify the Groups**: The groups given in the question are:
- I. `-NH3^+` (ammonium ion)
- II. `-NO2` (nitro group)
- III. `-CN` (cyano group)
- IV. `-COOH` (carboxylic acid)

2. **Understanding the -I Effect**:
- The -I effect is influenced by the electronegativity of the atoms in the substituent. More electronegative atoms will have a stronger -I effect.
- The order of -I effect generally follows the electronegativity of the atoms involved.

3. **Rank the Groups**:
- **-NH3^+**: The ammonium ion has a positive charge, which makes it a weak electron-withdrawing group due to the presence of nitrogen, but it is less effective compared to the others listed.
- **-NO2**: The nitro group is a very strong electron-withdrawing group due to the presence of both nitrogen and oxygen, making it highly electronegative.
- **-CN**: The cyano group is also a strong electron-withdrawing group due to the triple bond between carbon and nitrogen, which is quite electronegative.
- **-COOH**: The carboxylic acid group is also an electron-withdrawing group, but it is less effective than the nitro and cyano groups.

4. **Final Ranking**: Based on the analysis:
- The strongest -I effect is from the nitro group `-NO2`.
- Next is the cyano group `-CN`.
- Followed by the carboxylic acid group `-COOH`.
- Finally, the ammonium ion `-NH3^+` has the weakest -I effect.

Thus, the decreasing order of -I effect is:
**NO2 > CN > COOH > NH3^+**

### Final Answer:
The decreasing order of -I effect is:
**II > III > IV > I** (or `-NO2 > -CN > -COOH > -NH3^+`)

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