Amongest the halides
1. `BCl_(3)` , 2. `AlCl_(3)`
3. `GaCl_(3)` , 4. `InCl_(3)`
The order of decreasing Lewis acid character is

Options

A. 1,2,3,4
B. 4,3,2,1
C. 3,4,2,1
D. 2,3,4,1

Explanation

To determine the order of decreasing Lewis acid character among the halides BCl3, AlCl3, GaCl3, and InCl3, we need to analyze the Lewis acid character of each compound based on their ability to accept electrons.

### Step-by-Step Solution:

1. **Understanding Lewis Acids**:
- A Lewis acid is defined as an electron pair acceptor. The stronger the electron deficiency of the central atom, the stronger the Lewis acid character.

2. **Analyzing BCl3**:
- Boron in BCl3 has an empty p-orbital and is electron-deficient. However, BCl3 exhibits significant back-bonding due to the presence of chlorine, which can donate a lone pair of electrons to boron. This reduces the electron deficiency of boron, thereby decreasing its Lewis acid character.

3. **Analyzing AlCl3**:
- Aluminum in AlCl3 is also electron-deficient but does not have the same extent of back-bonding as BCl3 because both aluminum and chlorine are from the third period. Thus, back-bonding is less effective. Therefore, AlCl3 is a stronger Lewis acid than BCl3.

4. **Analyzing GaCl3**:
- Gallium in GaCl3 is similar to aluminum but is heavier and has a larger atomic radius. The back-bonding effect is still minimal, but GaCl3 is generally more electron-deficient than AlCl3. Thus, GaCl3 has a higher Lewis acid character than AlCl3.

5. **Analyzing InCl3**:
- Indium in InCl3 is the heaviest and has the least effective back-bonding due to its larger size and lower electronegativity. Therefore, InCl3 is the strongest Lewis acid among the four halides, as it has the least electron deficiency.

6. **Conclusion**:
- Based on the analysis, the order of decreasing Lewis acid character is:
- InCl3 > GaCl3 > AlCl3 > BCl3

### Final Answer:
**Order of decreasing Lewis acid character**: InCl3 > GaCl3 > AlCl3 > BCl3