JEE Main · 2026 · 04 Apr 2026 · Shift 2 · Chemical Bonding and Molecular Structure

With the internuclear axis along $z$, a $\pi$ molecular orbital is built by the sideways overlap of parallel $p$ orbitals that lie perpendicular to $z$ (the $p_x$ or $p_y$ orbitals). The bonding $\pi$ orbital arises from in-phase overlap, where the facing lobes carry the same sign. The antibonding ${\pi }^{\ast }$ orbital arises from out-of-phase overlap: the facing lobes carry opposite signs, so a nodal plane appears between the two nuclei (perpendicular to the bond) in addition to the nodal plane that contains the $z$-axis. The correct picture is the pair of side-by-side $p$ orbitals whose lobes are of opposite phase across the region between the atoms.