Geo-Scientist Prelims 2021 Chemistry Q18: Which one of the following is NOT a resonance structure of cyanate…

Which one of the following is NOT a resonance structure of cyanate (OCN⁻)?

1. (a) :Ö=C=N̈:⁻ (O two lone pairs, N two lone pairs, −1 on N)
2. (b) :Ö:⁻–C≡N: (O three lone pairs with −1, N one lone pair)
3. (c) :O⁺≡C–N̈:²⁻ (O one lone pair with +1, N three lone pairs with −2)
4. (d) :Ö=C=N:⁻ (O two lone pairs, N only one lone pair, −1 on N)