Decreasing - I effect of given groups is:
(i) `-CN " "` (ii) `-NO_2`
(iii) `-NH_2 " " ` (iv) `-Cl`

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 -I (minus I) effect of the given groups, we need to analyze each group based on its electronegativity and the ability to withdraw electrons from the carbon chain. The groups provided are:

1. -CN (cyano group)
2. -NO₂ (nitro group)
3. -NH₂ (amino group)
4. -Cl (chloro group)

### Step-by-Step Solution:

1. **Identify the Electronegativity of Each Group**:
- The -NO₂ group has nitrogen and oxygen, both of which are highly electronegative. This group strongly withdraws electrons.
- The -CN group has carbon triple-bonded to nitrogen, where nitrogen is also electronegative, leading to a significant electron-withdrawing effect.
- The -Cl group is a halogen and has a moderate electronegativity, allowing it to withdraw electrons but not as strongly as -NO₂ or -CN.
- The -NH₂ group has nitrogen, which is less electronegative compared to the other groups mentioned, and it can even donate electrons due to the lone pair on nitrogen.

2. **Rank the Groups Based on Their -I Effect**:
- The order of the -I effect is primarily determined by the electronegativity of the atoms involved and their ability to stabilize negative charge.
- The -NO₂ group has the strongest -I effect due to the high electronegativity of oxygen and the resonance stabilization it can provide.
- The -CN group follows as it also has a strong -I effect due to the electronegativity of nitrogen.
- The -Cl group comes next as it is a halogen and has a moderate -I effect.
- Finally, the -NH₂ group has the weakest -I effect as it can donate electrons due to the presence of a lone pair on nitrogen.

3. **Final Order of -I Effect**:
- Based on the analysis, the decreasing order of -I effect is:
1. -NO₂ (strongest)
2. -CN
3. -Cl
4. -NH₂ (weakest)

### Conclusion:
The decreasing -I effect of the given groups is:
**-NO₂ > -CN > -Cl > -NH₂**