JEE Main Chemistry Question (2026) — Solution

Step-by-step solution

In acetone (y), the carbon-oxygen bond is a localized double bond with a bond order of approximately 2. In the acetate ion (z), there are two equivalent resonance structures that delocalize the negative charge equally over both oxygen atoms. This results in a carbon-oxygen bond order of exactly 1.5. In tropone (x), the carbon-oxygen double bond is conjugated with the system of the seven-membered ring. Polarization of the C=O bond leads to a resonance structure with a single C-O^ - bond and a positive charge on the ring, forming an aromatic tropylium cation. This aromatic stabilization gives the C=O bond significant single-bond character. However, because this resonance structure involves charge separation, its contribution is less than that of the neutral structure. Thus, the bond order in tropone is between 1.5 and 2. Since bond length is inversely proportional to bond order, the carbon-oxygen bond length is longest for the acetate ion (bond order 1.5), followed by tropone (bond order between 1.5 and 2), and shortest for acetone (bond order 2). Therefore, the correct order of carbon-oxygen bond length is z > x > y. Answer: z>x>y