Which of the following molecules does NOT exhibit resonance? Select the correct answer below.

• A. NO3-
• B. CO3^{2-}
• C. H2O
• D. NO2-

Answer: (C)

Verified step by step guidance

1. Step 1: Understand what resonance means in chemistry. Resonance occurs when a molecule or ion can be represented by two or more valid Lewis structures (called resonance structures) that differ only in the placement of electrons, not atoms. This usually happens when there are conjugated pi bonds or lone pairs adjacent to multiple bonds.
2. Step 2: Analyze each molecule or ion given to see if resonance is possible. For resonance to occur, there must be delocalized electrons, typically in pi bonds or lone pairs adjacent to pi bonds.
3. Step 3: Consider \(\mathrm{NO_3^-}\) (nitrate ion). It has three oxygen atoms bonded to nitrogen with one double bond and two single bonds in resonance, allowing the negative charge to be delocalized over the oxygens. Therefore, \(\mathrm{NO_3^-}\) exhibits resonance.
4. Step 4: Consider \(\mathrm{CO_3^{2-}}\) (carbonate ion). Similar to nitrate, it has resonance structures where the double bond and negative charges are delocalized over the three oxygen atoms. So, \(\mathrm{CO_3^{2-}}\) exhibits resonance.
5. Step 5: Consider \(\mathrm{NO_2^-}\) (nitrite ion). It has resonance structures with the negative charge and double bond shifting between the two oxygen atoms, so it exhibits resonance. Now, consider \(\mathrm{H_2O}\) (water). It has no double bonds or adjacent lone pairs that can delocalize electrons, so it does NOT exhibit resonance.