Question

According to the Lewis concept, an acid is a substance which:
A.Accepts proton
B.Donates proton
C.Accepts a lone pair of electrons
D.Donates a lone pair of electrons

Answer 1

Lewis gave a theory to define acids and bases according to their properties of accepting a pair of electrons or donating a pair of electrons. According to Lewis's theory of acid-base reaction, acids are electron-pair acceptors and bases are electron-pair donors.

Complete step by step answer:
Lewis acids are the chemical species that have an empty orbital and can accept lone pairs of electrons from the Lewis bases.
Some of the examples of Lewis acids are Protons (hydrogen ion), cations of d-block elements, Cations of elements which form coordination compounds, etc.
Lewis base is the chemical species having highly localized HOMO (Highest Occupied Molecular Orbital). These chemical species can donate an electron pair to a Lewis acid.
Some of the most common Lewis bases are ammonia, alkyl amines, compounds having group 16 elements in -2 oxidation state, pyridine, and its derivatives, etc.
There are some compounds, for instance, water, they are considered to be both as Lewis base and Lewis acid. This is because of the reason that they can accept and donate lone pairs of electrons, based on the type of chemical reaction.

So, the correct answer is Option C.

Note:
There are three theories to define acid and base:
The Arrhenius Theory: It was given by Swedish chemist Svante Arrhenius. The theory describes acid as a compound that dissociates in water to give hydrogen cation whereas bases give hydroxyl ion.
The Bronsted-Lowry Theory: It was given by Johannes Bronsted and Thomas Lowry in1923. The theory described acid as a species that donates protons and bases are the species that accepts protons.
The Lewis acid-base theory: Given by Gilbert Lewis.