The Lewis acids are electron pair acceptors due to the availability of vacant orbitals they accept electrons from the donor compounds.
is a Lewis acid due to the unfilled valence shell on carbon atom (possessing positive charge) it accepts electron readily.
is not a Lewis acid due to the presence of negative charge which represents that there are electrons available for donation.
is not a Lewis acid due to the presence of lone pair on nitrogen which is easily donated to the acceptors.
is a Lewis acid due to the availability of vacant p-orbital on boron atom.
Hence, and
are Lewis acids.