Trihalides of boron are .............. compounds and act as Lewis ................

Explanation

To solve the question "Trihalides of boron are .............. compounds and act as Lewis ................", we can break it down into two parts.

### Step-by-Step Solution:

1. **Identify the Nature of Trihalides of Boron**:
- Boron trihalides (like BF3, BCl3, etc.) do not form ionic compounds. This is because boron has a high ionization enthalpy, which means it does not easily lose electrons to form cations. Instead, it prefers to share electrons with halogens (which are nonmetals) to form covalent bonds.
- Therefore, we conclude that trihalides of boron are **covalent compounds**.

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