Answer:
The atomic radius of atoms generally decreases from left to right across a period. There are some small exceptions, such as the oxygen radius being slightly greater than the nitrogen radius. Within a period, protons are added to the nucleus as electrons are being added to the same principal energy level.
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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.