Question

The nitrite ion is given by;
i. $ {[O - N = O]^ - } $
ii. $ {[N = O - O]^ - } $
Which of the structures represents possible resonance forms of this ion?
(A) Only i
(B) Only ii
(C) Both i and ii
(D) Neither i nor ii

Answer 1

Hint : To solve the given question there are certain rules of resonance that a molecule must follow like the hybridization of the structure must stay the same, only the electron moves which means the skeleton structure cannot be changed. Keeping these points in mind we will solve the given structure.

Complete Step By Step Answer:
Resonance, also called mesomerism, is a way of describing bonding in certain molecules or ions by the combination of several contributing structures into a resonance hybrid in valence bond theory.
It has particular value for describing delocalized electrons within certain molecules or polyatomic ions where the bonding cannot be expressed by one single lewis structure.
There are certain rule for resonance forms:
There is only one real structure for each molecule or ion. The resonance contributors are the exact same molecule or ion depicted in different ways.
Often resonance structures represent the movement of a charge between two or more atoms. In a resonance hybrid, the negative charge is spread over a larger part of the molecule and is therefore more stable.
Resonance contributors only differ by the positions of pi bond and lone pair electrons. Sigma bonds are never broken or made , because of this atom must maintain their same position.
All resonance contributors must have the same molecular formula, same number of electrons and same net charge.
Each atom should have a complete valence shell and charge.
Now keeping in mind these rules let’s solve the question.
First total number of valence electrons from $ Nitrogen $ is $ 5 $ and for $ Oxygen $ $ 12 $ . The charge is $ - 1 $ . Total valence electron is $ 18 $ . They will distribute to be sigma and pi bonds.
Now both the structures satisfy the valence electron. But in the second structure there is interchanging of the structure. As we have learned in the rules of resonance that skeleton structure cannot be changed, therefore only the first structure is correct.
Therefore our answer is option A.

Note :
Whenever such types of questions are asked first draw a lewis structure which will help in counting the valence electrons and therefore one can figure out the sigma and pi bond. Also make sure that the structure follows the rules of resonance.