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Q.
Which of the following is not Lewis acid?
Delhi UMET/DPMTDelhi UMET/DPMT 2002
Solution:
Electron deficient compounds or electron acceptors are Lewis acids.
(i) $ BF_{3}$ and $ AlCl_{3}$ are Lewis acids because B in $ BF_{3}$ and Al in $ AlCl_{3}$ are electron deficient atoms (They have 6 electrons each in their valence shell)
(ii) $ FeCl_{3}$ is Lewis acid because it can accept electrons in vacant d orbital.
(iii) $ N{{H}_{3}} $ is not Lewis acid because it has lone pair of electron (at N).
Infact it is Lewis base (there fore it is electron donor.)