* Boron (B) has three valence electrons.

* Chlorine (Cl) has seven valence electrons.

In BCl₃, boron forms three single bonds with three chlorine atoms, using all of its valence electrons. This leaves boron with no lone pairs of electrons.

VSEPR Theory:

The Valence Shell Electron Pair Repulsion (VSEPR) theory predicts the shape of molecules based on the repulsion between electron pairs around the central atom.

* Number of electron groups: BCl₃ has three electron groups (the three B-Cl bonds).

* No lone pairs: Boron has no lone pairs of electrons.

Conclusion:

Since there are three electron groups around boron and no lone pairs, the electronic geometry of BCl₃ is trigonal planar.