Which of the following is not a Lewis Base?
A.\[N{{H}_{3}}\]
B.\[{{O}^{2-}}\]
C.\[{{H}_{2}}O\]
D.\[{{I}^{+}}\]

Hint: We know that to answer this question you must recall the Lewis theory of acids and bases. The species that can accept an electron pair are termed as Lewis acids while those species which can donate a pair of electrons are known as a Lewis base. If a reaction involves the donation and acceptance of electrons then it must be a Lewis acid base reaction.

Complete answer: At first think about the definition of Lewis acid. A Lewis acid is a chemical species that contains an empty orbital that is capable of accepting an electron pair from a Lewis base to form a Lewis adduct.
The Lewis theory of acids and bases describes Lewis acids and Lewis bases as electron pair acceptors and donors respectively. Lewis acids are generally electron deficient substances or substances with the presence of empty orbitals and can thus accept electron pairs from a Lewis base. A Lewis base has the ability to donate a pair of electrons to a Lewis acid forming a coordinate covalent bond.
A Lewis base is generally a substance carrying an extra lone pair of atoms. The product formed when a Lewis base donates its electron pair to an acid is known as Lewis adducts. Lewis acid is defined as an electron pair acceptor and Lewis base is defined as an electron-pair donor. Lewis base is any species that has a filled orbital containing an electron pair that is not involved in bonding but may form a dative bond with Lewis acid to form Lewis adduct. So by that only option B is not having a lone pair.
Therefore, the correct answer is option B.

Note:
Remember that don’t get confused with the terms Lewis acid and Lewis base. Acid is used to accept electron pairs and Base is used to donate electron pairs. So usually a compound with a positive charge is acid and a compound with a negative charge is base.