NEET 2023, Chemistry Q25: Important Concepts Of Chemical Bonding

A Lewis acid is an electron-pair acceptor — it must have an empty orbital. Boron in ${\text{BF}}_3$ has only six electrons around it and a vacant $2p$ orbital, so it readily accepts a pair of electrons.

${\text{H}}_2\text{O}$, ${\text{OH}}^{-}$, and ${\text{NH}}_3$ all carry lone pairs and act as Lewis bases instead.