Question

How many resonance structures does $C{H_3}{O^ - }$ have?

Answer 1

Hint: The methoxide ion $C{H_3}{O^ - }$ is an anion formed by gaining one electron where the negative charge is localized at the oxygen atom. In the structure no double bond is seen. When the structure is not explained by one Lewis structure, then the resonance effect is seen.

Complete step by step answer:
Lewis structure is defined as a representation of the valence electrons around the atoms of the molecule. The Lewis structure of the compound is used to show how the electrons are placed around the atoms of the compounds. The valence electrons are shown as small dots.
When any ion or compound is not explained by one Lewis structure, two or more sets of Lewis structure are formed and this is known as resonance effect.
The resonance effect is defined as the sets of Lewis structure which describes the delocalization of electrons in a molecule.
The methoxide is an organic anion which behaves as the conjugate base of methanol. The chemical formula of methoxide ion is $C{H_3}{O^ - }$.
The Lewis structure of methoxide ion is shown below.

The negative charge of the anion is localized at the oxygen atom of the methoxide ion.
The structure of methoxide ion can be explained by one Lewis structure. So, no resonance structure is formed for methoxide ion $C{H_3}{O^ - }$.

Note:
The Lewis structure does not explain the geometry of the molecules, how the bonds are formed or how the valence electrons are shared between the atoms of the compound. The methoxide ion is a stronger base than hydroxide ions. It acts as a nucleophile.