Concept: Overlap of atomic orbitals is crucial for the formation of covalent bonds. The nature of this overlap (positive, negative, or zero) determines whether a bonding, antibonding, or non-bonding interaction occurs. Positive overlap leads to bond formation, while negative overlap leads to antibonding interactions, and zero overlap means no interaction.

Why (B) is correct:

Positive overlap occurs when the lobes of atomic orbitals with the same phase (sign of the wave function) overlap. This leads to an increase in electron density between the nuclei, forming a stable covalent bond.

• Option A: Shows the overlap of two s-orbitals. Both s-orbitals are spherical and have the same phase throughout. Their overlap is always positive, leading to a sigma bond.
• Option B: Shows the overlap of two p-orbitals where the lobes with opposite phases are overlapping. One lobe of the p-orbital is positive, and the other is negative. When a positive lobe of one p-orbital overlaps with a negative lobe of another p-orbital, it results in negative overlap. This leads to an antibonding interaction, not a positive overlap.
• Option C: Shows the side-on overlap of two p-orbitals where lobes of the same phase are overlapping. This is a positive overlap, leading to the formation of a pi bond.
• Option D: Shows the overlap of an s-orbital with a p-orbital. The s-orbital has a uniform phase, and it overlaps with one lobe of the p-orbital that has the same phase. This is a positive overlap, leading to a sigma bond.

Therefore, option B represents negative overlap, not positive overlap.

Correct Answer: (B)