In the following sets of resonance forms, label the major

Solution 40SP:

Here, we are going to find out the major and minor contributor structure of each molecules.

Step 1:

Resonance structures for a molecule would not have same energy.The stable resonance

forms are closer representations of the real molecule than less stable ones.

Here, in the first(minor) structures, all the atoms are octet except that central C atom which has nine electrons around it. On the other hand, in the second structures (major), all the carbon atoms are octet except the N atom which has nine electrons around it.

In the in the first(minor) structures, C atom has the negative charge and in the second structure N atom has negative charge on it . Nitrogen  is the more electronegative element, so the second structure is the major contributor.

(b)

Here, almost all the atoms are octet in both the structures and negative charge is on the Oxygen atom. Therefore major contributing structure would be that which have minimum charge separation.

Thus, Structure II( Major II) is the major contributing structures.

(c)

Here, second (major II)  and third (major III) structures are major. This is because negative charge is on Oxygen atom.