Question

Proton donor is:
(A) Arrhenius acid
(B) Arrhenius base
(C) Lewis acid
(D) Lewis base
(E) Bronsted-Lowry acid

Answer 1

Hint: Before answering this question we should know that proton donors are always acids. They donate a hydrogen atom which basically contains one proton.

Complete step-by- step answer:
The reaction between an acid and base is essentially a proton transfer wherein an acid donates a proton and a base accepts it.
Let us now take a look at the various theories given as options.
Arrhenius theory is based on the fact that acid produces hydrogen ion and bases produces hydroxyl ion on dissociation. An aqueous medium is mandatory in this regard hence Arrhenius failed to explain the basic nature of ammonia gas.
On the other hand, Lewis definitions of acid and bases illustrate the concepts of electron pair donation and acceptance. A Lewis base is an electron donor while Lewis acid is electron acceptor.
One advantage of the Lewis theory is the way it complements the model of oxidation-reduction reactions. Oxidation-reduction reactions involve a transfer of electrons from one atom to another, with a net change in the oxidation number of one or more atoms.
In the Bronsted-Lowry Theory what makes a compound an acid is whether or not it accepts protons. A substance cannot act as an acid without the presence of a base to accept the proton. The determination of a substance as a Bronsted-Lowery acid or base can only be done by observing the reaction. 
Hence, a Bronsted Lowry acid is always a proton donor and the base is a proton acceptor.

Thus, the correct answer is Option (E) Bronsted-Lowry acid.

Note: Thus we should remember that Bronsted-Lowry acid is a chemical compound that donates one or more hydrogen ions in a reaction. An acid and a base pair which differ only by a single proton is called a conjugate acid-base pair.