Boron halides behave as Lewis acid because of their ___ nature.

Options

A. Ionisation property
B. Electron deficient nature
C. Acidic nature
D. Covalent nature

Answer

To answer the question "Boron halides behave as Lewis acid because of their ___ nature," we can follow these steps:

### Step-by-Step Solution:

1. **Understanding Boron Halides**:
Boron halides include compounds like BF3 (boron trifluoride), BCl3 (boron trichloride), BBr3 (boron tribromide), and BI3 (boron triiodide).

2. **Electronic Configuration of Boron**:
The electronic configuration of boron is 1s² 2s² 2p¹, which means boron has a total of 5 electrons in its outer shell.

3. **Hybridization and Bonding**:
When boron forms bonds with halogen atoms, it promotes one of its 2s electrons to a 2p orbital to form three equivalent sp² hybrid orbitals. This results in a configuration of 2p_x¹ 2p_y¹, indicating that it can form three covalent bonds with halogens.

4. **Formation of Boron Halides**:
In BF3, for example, boron shares one electron with each of the three fluorine atoms. However, after forming these bonds, boron only has 6 electrons in its valence shell (3 from the bonds with fluorine), which means it does not have a complete octet.

5. **Electron Deficiency**:
Since boron has only 6 electrons, it is considered electron deficient. This deficiency means that boron has a tendency to accept electrons from other species to complete its octet.

6. **Lewis Acid Behavior**:
According to the Lewis theory, Lewis acids are defined as species that can accept an electron pair. Because boron halides are electron deficient, they readily accept electrons from other molecules, thus behaving as Lewis acids.

7. **Conclusion**:
Therefore, the correct answer to the question is that boron halides behave as Lewis acids because of their **electron deficient nature**.

### Final Answer:
Boron halides behave as Lewis acids because of their **electron deficient nature**.

---