1.

How many resonating structures can be drawn for `NO_2`?A. SixB. FourC. FiveD. Two

Answer» Correct Answer - B
Since `NO_2` has `5+(2xx6)=17` valence electrons, an odd number, not all of its atoms can have complete octets. Without considering nonbonding electrons, we can write two structures:
`O=N-OiffO-N=O`
In distributing the nonbonding electrons, we can write structures in which N atom has an incomplete octet and has the unpaired (or odd) electron:
`overset(..)underset(..)O=underset(I)overset(.)N-overset(..)underset(..)O:iff:overset(..)underset(..)O-overset(.)underset(II)N=underset(..)overset(..)O`
or structures in which the O atoms have incomplete octet, such as
`overset(.)underset(..)O=underset(III)overset(..)N-overset(..)underset(..)O:iff:overset(.)underset(..)O-underset(IV)overset(..)N=overset(..)underset(..)O`
The first two structures, in which the N atom has an incomplete octet, make the most important contribution. Structures such as the last ones, in which the O atom has incomplete octet, are less important, since the most electronegative element usually has the completed octet.


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