Question

Bronsted-lowry acids is:
A. a proton acceptor
B. an electron acceptor
C. an electron donor
D. a proton donor

Answer 1

Classical concept of acid base is explained by different theories, bronsted lowry concept of acids-bases is one of them which was given by bronsted and lowry independently and simultaneously.

Complete answer:
An acid here is defined as a substance that has a tendency to give a proton H and a base is defined as a substance which has a tendency to accept a proton. In other words, an acid is a proton donor whereas a base is a proton-acceptor. Examples of bronsted acids are HCl and acetic acid in the reactions below as they are donating a proton to water,
$HCl + {H_2}O \rightleftharpoons {H_3}{O^ + } + C{l^ - } \\\ C{H_3}COOH + {H_2}O \rightleftharpoons {H_3}{O^ + } + C{H_3}CO{O^ - }$
The bronsted-lowry definitions of acid and base is not restricted to molecules but is applicable to ions as well. A conjugate pair of acid and a base differs by a proton only. In the above reactions we can say that both the reactions contain two conjugate pairs which are HCl - $C{l^ - }$ and ${H_2}O$-${H_3}{O^ + }$.
Substances like $B{F_3}, AlC{l_3}$ etc. do not have any hydrogen and hence cannot give a proton but are known to behave as acids which result to be a limitation to the above concept.

Therefore from above we can conclude that the correct option is D.

Note: All Arrhenius acids are also bronsted acids but all Arrhenius bases are not bronsted bases as an Arrhenius acid can give a $H^+$ ion whereas bronsted acid donates a proton which is again $H^+$ ion. On the other hand bronsted base accepts a proton and Arrhenius base gives $OH^-$ ions in the solution.