The decreasing order of `- I` effect of the orbitals is :
(I) `sp`
(II) `sp^2`
(III) `sp^3`.

Options

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

Explanation

To determine the decreasing order of the -I (negative inductive) effect of the orbitals sp, sp², and sp³, we need to understand the relationship between the s-character of these orbitals and their ability to withdraw electrons.

### Step-by-Step Solution:

1. **Understanding the Inductive Effect**:
- The -I effect refers to the electron-withdrawing ability of atoms or groups. It is influenced by the hybridization of the orbitals involved.
- More s-character in an orbital means a stronger ability to withdraw electrons.

2. **Identifying the s-Character of Each Orbital**:
- **sp Hybridization**: Contains 50% s-character and 50% p-character.
- **sp² Hybridization**: Contains 33.33% s-character and 66.67% p-character.
- **sp³ Hybridization**: Contains 25% s-character and 75% p-character.

3. **Comparing the s-Character**:
- Since sp has the highest s-character (50%), it will have the strongest -I effect.
- Next is sp² with 33.33% s-character, which will have a moderate -I effect.
- Finally, sp³ has the least s-character (25%) and thus the weakest -I effect.

4. **Arranging in Decreasing Order**:
- Based on the s-character, the decreasing order of the -I effect is:
- **sp > sp² > sp³**

### Final Answer:
The decreasing order of -I effect of the orbitals is:
**sp > sp² > sp³**