Explanation:
Carbon dioxide is a polar molecule whose positive center is on the carbon atom: This positive center is able to attract (and accept) the lone electron pairs present on the oxide ion (O2-). carbon dioxide is acts as a Lewis acid
A Lewis acid can accept a pair of electrons from a Lewis base. The boron in BF3 is electron poor and has an empty orbital, so it can accept a pair of electrons, making it a Lewis acid. A Lewis acid is defined as an electron-pair acceptor.
In CO molecule, there is a lone pair on both carbon and oxygen. The substance which can donate an electron pair are called Lewis base. It is clear that CO molecule can donate an electron pair and hence, it is a Lewis base. Also, CO can be BOTH a Lewis acid and base.
Oxygen is a Lewis base (that too a weak one), not a Lewis acid. REASON: It has lone pair of electrons, which can be donated to electron-deficient species (Lewis acids).
Methane is Neither a Lewis Acid or Lewis Base.
