In which year did Langmuir reform the Lewis concept by abandoning the idea of a stable cubical arrangement of the octet and introducing the term ‘covalent bond’?

Correct option is A

Irving Langmuir reformulated the Lewis concept in 1919 by introducing the term "covalent bond" and abandoning the idea of a stable cubical arrangement of the octet. Therefore, the correct option is (a) 1919.
· Kössel and Lewis in 1916 developed an important theory of chemical combination between atoms known as the electronic theory of chemical bonding.
· When two atoms share one electron pair they are said to be joined by a single covalent bond.