Question

All Lewis acids are not necessarily_____________.
A. Proton acceptor
B. Bronsted acids
C. Arrhenius bases
D. Electrophile

Answer 1

An acid is a molecule which is capable of donating a proton and base is a molecule which is capable of accepting a proton. Electrophile are those compounds which are electron deficient and Nucleophile are those compounds which are electron rich.

Complete step by step solution:
Firstly we have to know the definition of these acids and bases to solve this question.
Lewis Acid: These are the chemical species which have empty orbitals and are able to accept a lone pair of electrons. They are classified as electrophile. Examples are ${H^ + }$,$BF_3$,$CO_2$.
Lewis Base: These are the chemical species that have the ability to donate an electron pair to a given Lewis acid. Lewis bases are electron rich species that is why they can be classified as nucleophiles. Example is: $NH_3$
Arrhenius acids: These are those acids which donate in aqueous solution. Examples are: $HCl$ , $H_2SO_4$
$HCl(aq) \to {H^ + }(aq) + C{l^ - }(aq)$
Arrhenius bases: These are those bases which donate $O{H^ - }$ in aqueous solution. Examples are: $NaOH$
Bronsted Lowry acids: It is a substance which donates a proton or ${H^ + }$ion to other compounds.
Acids↔ Proton+ Conjugate base
$HF$↔${H^ + }$+${F^ - }$
Bronsted Lowry bases: It is a substance which accepts a proton or ${H^ + }$ion from other compounds.
Examples are: $NH_3$
Now let us move to question and we see that all Lewis acids are proton acceptors but Bronsted acids are those which accept ${H^ + }$ion.
So all Lewis acids are not necessarily Bronsted acids.

**Hence our correct option is B.

Note:**
This is the most confusing question for students but a clear concept of all types of acids can clear all our doubts. Lewis acids are electron deficient so they can be called as electrophiles and they are just proton acceptors.