Question

The species showing resonating structures are:
A.$HCO{O^ - }$
B.$HCOOH$
C.$N{O_2}$
D.$S{O_3}$

Answer 1

Hint: To answer this question, we must be familiar with resonating structures. In any molecule or ion exhibiting resonance, there are a few resonating structures whose average defines the given species.

Complete answer:
We know that resonance describes the bonding of atoms in a certain molecule or ion by merging various contributing forms, which are known as resonating structures or canonical structures, in accordance to the valence bond theory into a resonance hybrid. Resonating structures are Lewis structures that show the delocalization of electrons in a molecule or ion.
The delocalization of electrons takes place by means of fractional bonds and partial formal charges in a resonance hybrid. All resonating structures are not equivalent and to determine the structure of the compound, we need to predict the most stable resonating structure. The more stable a structure is, greater is its contribution to the hybrid.
The compounds in options A, C and D all show resonating structures.
Meanwhile formic acid given in option B, does not show resonating structure as when electrons are delocalized onto the hydroxyl oxygen, the number of electrons on the oxygen atom exceeds the valency of the oxygen atom. Therefore, formic acid has no significant resonance.

The correct answers are A, C and D.

Note:
The stability of a resonance structure varies as follows due to certain factors:
More the number of covalent bonds, higher is the stability
Structures in which all the atoms have a complete valence shell are stable and make large contributions to the hybridCharge separation in the molecule decreasing the stability.
Negative charge on more electronegative atoms rather than the less electronegative atom increases the stability.