Question

Which of the following is Lewis acid?
A) \[N{H_3}\]
B) \[N{H_4}^ + \]
C) \[B{F_3}\]
D) \[{H_2}O\]

Answer 1

Hint: We need to know that a Lewis acid is a substance that accepts a pair of electrons to form a covalent bond. A Lewis base is a substance that donates a pair of electrons to form a covalent bond. So, a Lewis acid-base reaction is represented by the transfer of a pair of electrons from a base to an acid.

Complete answer:
We will look at all the options one by one to answer this question:
Option A) this option is incorrect as ammonia is a Lewis base and not a Lewis acid, It will donate electrons to compounds that will accept them.
Option B) this option is incorrect as \[N{H_4}^ + \] is neither a Lewis Base nor a Lewis acid because it does have any available lone pair of Electrons to donate so that it can said to be a Lewis base, but also because it's octet is complete it doesn't have enough vacancy to accept any electron pair from other Lewis base, which means that it cannot be called a Lewis acid.
Option C) this option is correct as \[B{F_3}\] acts as a Lewis acid when it accepts the lone pair of electrons that \[N{H_3}\] donates.
Option D) this option is incorrect as water is a Lewis base.

So, the correct answer is “Option C”.

Note:
We have to remember that a Lewis base is any substance, such as the OH- ion, that can donate a pair of nonbonding electrons. A Lewis base is therefore an electron-pair donor. In the Lewis theory, an acid is any ion or molecule that can accept a pair of nonbonding valence electrons.