Question

According to Lewis concept, an acid is a/an:
A. proton donor
B. electron pair donor
C. proton acceptor
D. electron pair acceptor

Answer 1

Hint: Several theories on acids and bases were introduced based on \[{{\text{H}}^ + }\] ions, ${\text{O}}{{\text{H}}^ - }$ ions, electron donating or accepting. Lewis concept is the broadest definition of acids and bases, and only one to not emphasize bare protons, though it can include them. It often overlaps with other theories.

Complete step by step answer:
There are three definitions of acids and bases. The theory has changed over time due to research and experimentation. They are:
1.Arrhenius theory
This theory is based on producing hydroxide or hydrogen cations when dissolved in water. Acids produce \[{{\text{H}}^ + }\] ions while bases produce ${\text{O}}{{\text{H}}^ - }$ ions in aqueous medium. Aqueous solutions are liquids in which the molecules are dissolved in water.
2.Bronsted-Lowrey
It is a broader definition than Arrhenius. Acid is a hydrogen-ion donor and base is a hydrogen-ion acceptor. Acids and bases always come in pairs.
A conjugate base is the charged particle of the original acid, after it donates its hydrogen ion. A conjugate acid is the charged particle formed when the original base gains a hydrogen ion. Thus a conjugate acid-base pair is related by the loss or gain of a single hydrogen ion.
3.Lewis theory
Lewis concept is based on the donation or acceptance of a pair of electrons during a reaction. Lewis acid is an electron pair acceptor and base is an electron pair donor. Most general of all these definitions, acids don’t even need hydrogen.
E.g. ${\text{S}}{{\text{O}}_2} + {{\text{O}}^{2 - }} \to {\text{S}}{{\text{O}}_3}^{2 - }$
Lewis acid Lewis base

Hence option D is correct.

Additional Information:
Acids are generally sour in taste. They can conduct electricity. They react with metals to produce hydrogen gas. They change the color of indicators. They react with bases to form salt and water. They have ${\text{pH}}$ less than $7$ .

Note:
Not all acid-base reactions involve proton transfer. Acids form a covalent bond by accepting electrons and bases form covalent bonds by donating electrons. Neutralization is the formation of a covalent bond between an acid and a base reactant. An adduct is formed between Lewis acids and bases resulting in a single product containing all atoms of all products.