KCET 2026 Chemistry Solved Paper

Concept:Resonance structures differ only in the arrangement of electrons, not in the positions of atoms, and the actual ion is a resonance hybrid.Explanation:In $\mathrm{CO}_{3}^{2-}$, carbon is the central atom bonded to three oxygen atoms.Three resonance structures are possible because the $\pi$ bond can be placed between carbon and any one of the three oxygen atoms.Thus, statement (b) is correct.The actual carbonate ion is a resonance hybrid of these three structures.As a result, all three $\mathrm{C}-\mathrm{O}$ bonds become equivalent in length and strength, intermediate between a single and a double bond.Hence, statement (a) is correct.Statement (c) is incorrect because resonance structures do not change the positions of atoms; only the positions of $\pi$ electrons and lone pairs change.Statement (d) is incorrect because the formal charge on carbon is $0$, not $-2$.Using the formal charge formula: $$\text{Formal charge} = \text{valence electrons} - \text{non-bonding electrons} - \frac{1}{2}(\text{bonding electrons})$$For carbon: $$4 - 0 - \frac{8}{2} = 4 - 4 = 0$$Therefore, the correct statements are (a) and (b) only.Answer:Option B: a and b only.