Question

An acid is a substance which:
(A) Accepts a lone pair of electrons (Lewis concept)
(B) Donates a proton (Lowry and Bronsted concept)
(C) Acts as an acid only in presence of a conjugate base
(D) None of the above

Answer 1

Chemical substances are classified into three types based on nature. They are acids, bases, and neutral substances. Lewis and Bronsted are the two theories that classified chemical substances. Lewis theory is based on electron pairs and the Lowry and Bronsted concept is based on the proton.

Complete answer:
Lewis theory was discovered by scientist Lewis and this theory is based on electron pairs.
Any chemical substance that can accept an electron pair is known as an acid or lewis acid.
Any chemical substance that can donate an electron pair is known as a base or lewis base.
Lowry and Bronsted theory is based on protons.
Any chemical substance that can donate a proton is known as an acid or Bronsted acid.
Any chemical substance that can accept a proton is known as base or Bronsted base.
Thus, from these two theories, an acid is a substance that can accept an electron pair and donate a proton.
Options A and B are the correct options.

Note:
Water consists of two ions namely hydrogen ion which can be known as a proton, and hydroxide ion. The chemical substance that can release a proton is simply an acid. So, acid strength depends upon the releasing capability of the proton. Strong acid can release a proton easily.