The highest occupied molecular orbital for Ne₂ is:

Solution & Explanation

Concept: Build the molecular-orbital (MO) energy diagram and fill electrons; the HOMO is the highest-energy orbital that contains electrons. Step 1 — Count electrons: each Ne atom has 10 electrons, so Ne₂ has 20 electrons. Step 2 — For O₂/F₂/Ne₂ (no s–p mixing) the filling order is: σ1s, σ*1s, σ2s, σ*2s, σ2p_z, (π2p_x = π2p_y), (π*2p_x = π*2p_y), σ*2p_z. Step 3 — Fill 20 electrons: σ1s² σ*1s² (4) → σ2s² σ*2s² (8) → σ2p_z² (10) → π2p_x² π2p_y² (14) → π*2p_x² π*2p_y² (18) → σ*2p_z² (20). Step 4 — All bonding and antibonding 2p MOs are completely filled; the LAST (highest-energy) filled orbital is σ*2p_z. So the highest occupied molecular orbital of Ne₂ is σ*2p → answer D. (Consistent with bond order = (10 − 10)/2 = 0, i.e. Ne₂ does not exist as a stable molecule.)