JEE Advanced levelSingle correct optionDifficulty 3 of 3cb050
Assertion (A): All three C-O bonds in COX3X2− have the same length.
Reason (R): The carbonate ion rapidly flips among three structures, each with different C-O bond lengths.
ABoth A and R are true and R is the correct explanation of A
BBoth A and R are true but R is not the correct explanation of A
CA is true but R is false
DA is false but R is true
Answer: C
A is true: delocalisation makes the three bonds equal (bond order 4/3). R is false: the canonical structures are only contributors to one real hybrid; the ion does not interconvert among them.