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KCET · Chemistry · Chemical Bonding and Molecular Structure

With respect to resonance structures of \(\text{CO}_3^{2-}\) ion, which of the following statements are correct?
(a) All \(\text{C}-\text{O}\) bonds in \(\text{CO}_3^{2-}\) are equivalent
(b) There are three resonance structures possible for \(\text{CO}_3^{2-}\) ion
(c) The position of carbon and oxygen should change in every resonance structure
(d) The formal charge on carbon atom is \(-2\)

  1. A a, b and c
  2. B a and b only
  3. C b and d only
  4. D a, b and d
Verified Solution

Answer & Solution

Correct Answer

(B) a and b only

Step-by-step Solution

Detailed explanation

The carbonate ion, \(\text{CO}_3^{2-}\), has three equivalent resonance structures where the double bond is shared among the three oxygen atoms.

Due to resonance, all three \(\text{C}-\text{O}\) bonds have partial double bond character and are equivalent in length and strength. Thus, statement (a) is correct.

There are exactly three equivalent resonance structures for the \(\text{CO}_3^{2-}\) ion. Thus, statement (b) is correct.

In resonance structures, the positions of the atoms must remain fixed; only the arrangement of electrons changes. Thus, statement (c) is incorrect.

The formal charge on the carbon atom in \(\text{CO}_3^{2-}\) is calculated as: Formal charge = (Valence electrons) - (Non-bonding electrons) - (Bonding electrons)/2 = \(4 - 0 - \dfrac{8}{2} = 0\). Thus, statement (d) is incorrect.

Therefore, only statements (a) and (b) are correct.

Answer: a and b only