Decreasing `-I` effect of given is:
(i) `CN` , (ii) `NO_(2)`
(iii) `NH_(2)` , (iv) `F`

Options

A. `iii gt ii gt i gt iv`
B. `ii gt iii gt iv gt i`
C. `iii gt ii gt iv gt i`
D. `ii gt i gt iv gt iii`

Explanation

To determine the decreasing order of the -I (negative inductive) effect of the given groups, we need to analyze the electronegativity and the ability of each group to withdraw electron density from the rest of the molecule. The groups provided are CN (cyano), NO₂ (nitro), NH₂ (amino), and F (fluoro).

### Step-by-Step Solution:

1. **Identify the Groups and Their Electronegativity:**
- CN (cyano): The nitrogen in the cyano group is electronegative and can withdraw electron density.
- NO₂ (nitro): The nitro group has resonance structures where the electronegative oxygen atoms can pull electron density away from the molecule.
- NH₂ (amino): The amino group has nitrogen, which is less electronegative than oxygen and does not have a significant inductive effect.
- F (fluoro): Fluorine is the most electronegative element and has a strong -I effect.

2. **Rank the Groups Based on Their -I Effect:**
- **NO₂**: This group has a strong -I effect due to the presence of two electronegative oxygen atoms and resonance structures that stabilize the negative charge.
- **CN**: The cyano group also has a significant -I effect due to the electronegativity of nitrogen, but it is less than that of NO₂.
- **F**: Although fluorine is highly electronegative, its -I effect is less pronounced compared to NO₂ and CN because it is a single atom and does not have resonance stabilization.
- **NH₂**: The amino group has the weakest -I effect among these groups because nitrogen is less electronegative and does not have a charge to withdraw electron density effectively.

3. **Final Order:**
Based on the analysis, the decreasing order of the -I effect is:
- NO₂ > CN > F > NH₂