Question

The resonating structures of cyanate ions are:
 $ O = C = {N^ - } \leftrightarrow O{}^ - - C \equiv C - N \leftrightarrow {O^ + } \equiv C - {N^{2 - }} $
The correct set of oxidation states of O,C and N respectively with the most stable structure out of the above is:
(i) $ - 3, + 4, - 2 $
(ii) $ - 2, + 4, - 3 $
(iii) $ - 1, + 4, - 3 $
(i) $ 0, + 4, - 5 $

Answer 1

Hint: The cyanate ion is an ambidentate ligand. Also, the structures which show the combination in different ways are called the canonical structures or the resonating structures.

Complete solution
When we talk about chemistry we come to know that the resonating structures further the structures which show the combination in different ways are called the canonical structures or the resonating structures. Now here we are talking about the cyanate ions so we find out that the cyanate ion is an ambidentate ligand that further forms complexes with a metal ion in which the either nitrogen or oxygen atom may be the electron pair donor and further helps as an bridging ligand. Talking about the question we will discuss each resonating structure and its contribution.
So talking about the first one we come to know that is further shown below:
 $ O = C = {N^ - } $ in this the electron gets exchanged between oxygen and carbon and is a double bond and further oxygen has $ - 2 $ charges.
Then we will consider the second equation:
 $ O - C \equiv N $ here the carbon atom sharing is done between oxygen and nitrogen of four electrons hence, we can say there are four valencies of electrons that further means that the carbon atom has $ + 4 $ charges.
Lastly talking about the third resonating structure:
 $ O \equiv C - {N^{2 - }} $ here in this the nitrogen atom is sharing one electron and also there are $ - 1 $ and $ - 2 $ charges already present ten further it will become $ - 3 $ charges on nitrogen atom.

Note
Here after the discussion we found that the correct option is option B . Here we should take care while making the resonance structures that the electron in pi bonding or the non bonding electrons easily participate in resonance.