The central atom in BCl3 is boron (B). Here's how to determine its hybridization:

1. Count the number of electron domains around the central atom:

* Boron has 3 valence electrons.

* Each chlorine atom contributes 1 electron for bonding.

* Total electron domains around boron = 3 (3 bonds)

2. Relate the number of electron domains to the hybridization:

* 3 electron domains correspond to sp² hybridization.

Therefore, the hybridization of boron in BCl3 is sp².

Explanation:

* In sp² hybridization, one s orbital and two p orbitals of the central atom combine to form three hybrid orbitals.

* These hybrid orbitals are arranged in a trigonal planar geometry, which is the shape of BCl3.