Identify a species which is not a Bronsted acid but a Lewis acid

Step-by-step solution

Bronsted defined an acid as a substance, which has a tendency to give a proton ( H ⁺ ) , on the other hand, Lewis proposed an acid as a substance, which is capable of accepting a pair of electrons. As ₃ H ⁺ , NH ₃ and HCl has H ⁺ ions, these are Bronsted acids whereas BF ₃ is an electron deficiet molecule, thus be have like a Lewis acid, i.e., electron pair acceptor.