Looking for classes? Ksquare Career Institute, Bengaluru →
Which of the following is least likely to behave as Lewis base?
A
$OH^-$
B
$H_2O$
C
$NH_3$
D
$BF_3$
Detailed Solution
A Lewis base is a species that can donate a lone pair of electrons.
$OH^-$ and $H_2O$ have lone pairs on oxygen, and $NH_3$ has a lone pair on nitrogen, so all three act as Lewis bases.
In $BF_3$, boron has only six electrons in its valence shell and an empty p orbital; it is electron deficient.
$BF_3$ therefore accepts an electron pair and behaves as a Lewis acid, not as a Lewis base.
Hence $BF_3$ is least likely to behave as a Lewis base.
$OH^-$ and $H_2O$ have lone pairs on oxygen, and $NH_3$ has a lone pair on nitrogen, so all three act as Lewis bases.
In $BF_3$, boron has only six electrons in its valence shell and an empty p orbital; it is electron deficient.
$BF_3$ therefore accepts an electron pair and behaves as a Lewis acid, not as a Lewis base.
Hence $BF_3$ is least likely to behave as a Lewis base.