Question

Identify the species having one \(\pi\)-bond and maximum number of canonical forms from the following:

• A. SO\(_3\)
• B. O\(_2\)
• C. SO\(_2\)
• D. CO\(_3^{2-}\)

Hint:

The more resonance structures a molecule can have, the more stable it is, as electron density is spread out over the molecule.

Answer 1

The Correct Option is D

Step 1: {Analysis of Canonical Forms} 
Canonical forms are the different resonance structures that a molecule can have, resulting in delocalization of electrons. The species with the maximum number of canonical forms has the most stable resonance structure. 
Step 2: {Analysis of Compounds} 
SO\(_3\) has three resonance structures but lacks a \(\pi\)-bond between sulfur and oxygen in each structure.
O\(_2\) has two resonance structures with a single \(\pi\)-bond between the two oxygen atoms, but it doesn’t have the maximum number of canonical forms.
SO\(_2\) has two resonance structures, but again, it doesn’t maximize the number of canonical forms.
CO\(_3^{2-}\) has three resonance structures, each with a \(\pi\)-bond and delocalized electrons between the carbon and the oxygen atoms. 
The carbonate ion (CO\(_3^{2-}\)) has the maximum number of canonical forms.
Thus, the correct answer is (D). 
 

Answer 2

Step 1: Understand what a canonical form is
Canonical forms (or resonance structures) are different valid Lewis structures for a molecule or ion that differ only in the arrangement of electrons (especially π-bonds and lone pairs), not in the arrangement of atoms.

Step 2: Examine the structure of CO₃²⁻ (carbonate ion)
CO₃²⁻ consists of one carbon atom bonded to three oxygen atoms.
- It has a total of 24 valence electrons.
- One C=O double bond and two C–O single bonds are possible.
- Due to resonance, the double bond is delocalized over all three oxygen atoms.
- This gives rise to **three equivalent canonical forms**.
- The molecule contains **one delocalized π-bond** across the C–O bonds.

Step 3: Compare with other options (if provided)
Other similar species might have either fewer canonical forms or more than one π-bond, but CO₃²⁻ is unique in having exactly **one π-bond (delocalized)** and **maximum canonical forms (three)** among common small ions.

Step 4: Conclusion
CO₃²⁻ has one π-bond (delocalized) and the maximum number of resonance structures (canonical forms).

Final Answer: CO₃²⁻