The extent of overlapping between atomic orbitals depends on their shape, directionality, and energy. For effective overlapping, the orbitals must have comparable energies and proper orientation.

Concept: The extent of orbital overlap determines the strength of the covalent bond. Generally, p-p orbital overlap is more effective than s-s or s-p overlap due to the directional nature of p-orbitals.

Why (B) is correct:

• 2p-2p overlap: p-orbitals are directional and dumbbell-shaped. When two p-orbitals overlap head-on (axial overlap), they form a strong sigma bond. When they overlap sideways (lateral overlap), they form a pi bond. The directional nature allows for a greater extent of overlap compared to spherical s-orbitals. Among the given options, the head-on overlap of two 2p orbitals (forming a sigma bond) provides the maximum effective overlap area between the nuclei.

Option Analysis:

• (A) 2s-2s overlap: s-orbitals are spherical and non-directional. Their overlap is less effective than p-p overlap because the electron density is spread out spherically, leading to a smaller concentrated overlap region between the nuclei.
• (C) 2s-2p overlap: This involves an s-orbital and a p-orbital. While overlap occurs, it is generally less effective than p-p overlap due to the difference in shape and directionality. The overlap region is not as concentrated as in a head-on p-p overlap.
• (D) Both (A) and (C): Since 2p-2p overlap is the most effective, this option is incorrect.

Correct Answer: (B)