Why boron trihalides act as Lewis acids ?

Explanation

**Step-by-Step Solution:**

1. **Understanding Lewis Acids:**
- Lewis acids are defined as species that can accept an electron pair. This means they have a tendency to form bonds by accepting electrons from other species.

2. **Identifying Boron Trihalides:**
- Boron trihalides are compounds of boron with halogens, represented as BX3, where X can be fluorine (F), chlorine (Cl), bromine (Br), or iodine (I).

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