Which of the following statement is correct?

Anti-bonding MOs have higher energies than highest energy atomic orbitals from which they are formed.

The correct answer is option 2. Anti-bonding MOs have higher energies than highest energy atomic orbitals from which they are formed.

Let us delve deeper into each of the statements regarding molecular orbitals (MOs) and explain why each is correct or incorrect.

1. Non-bonding orbitals have the same energy as the bonding MOs.

This statement is incorrect. Non-bonding orbitals are atomic orbitals that are not involved in bonding interactions. Their energy levels are typically the same as the atomic orbitals from which they originate. Bonding molecular orbitals, on the other hand, are formed by the constructive combination of atomic orbitals, resulting in a lower energy level compared to the original atomic orbitals. Therefore, non-bonding orbitals do not have the same energy as bonding MOs; they generally have energy levels close to the original atomic orbitals.

2. Anti-bonding MOs have higher energies than the highest energy atomic orbitals from which they are formed.

This statement is correct. Anti-bonding molecular orbitals are formed by the destructive combination of atomic orbitals, which results in an increase in energy. The anti-bonding orbital is higher in energy than the atomic orbitals that combined to form it. This is because the destructive interference creates a node between the nuclei, which raises the energy of the electrons in the anti-bonding MO.

3. Bonding orbitals have higher energies than the anti-bonding MOs.

This statement is incorrect. Bonding molecular orbitals are lower in energy compared to the atomic orbitals from which they are formed due to constructive interference, which leads to a more stable configuration. Anti-bonding orbitals, conversely, are higher in energy because of destructive interference. Therefore, bonding orbitals have lower energies, not higher, compared to anti-bonding orbitals.

4. All are correct.

This statement is incorrect because, as explained, not all the previous statements are correct. Only the second statement about anti-bonding MOs having higher energies than the highest energy atomic orbitals is correct.

To summarize:

Bonding Molecular Orbitals: Formed by constructive interference, lower in energy than the original atomic orbitals.

Anti-Bonding Molecular Orbitals: Formed by destructive interference, higher in energy than the original atomic orbitals.

Non-Bonding Orbitals: Have energy levels similar to the original atomic orbitals and do not participate in bonding or anti-bonding interactions.

Given this understanding, the correct statement is: (2) Anti-bonding MOs have higher energies than the highest energy atomic orbitals from which they are formed.