Electron configuration and orbital shapes in ground-state carbon

Steps:

• Carbon (Z=6) has electron configuration 1s² 2s² 2p² in ground state.
• Occupied orbitals are 1s, 2s (spherical), and 2p (dumbbell-shaped).
• Energy levels are n=1 (1s) and n=2 (2s, 2p), totaling two levels.
• Lowest energy orbital is 1s (spherical); highest is 2p (not spherical).

Why D is correct:

• The 1s orbital is the lowest energy occupied orbital, and s orbitals are spherical by quantum mechanical definition.

Why the others are wrong:

• A: Only two energy levels (n=1 and n=2), not four.
• B: Four electrons in s orbitals (1s² 2s²) vs. two in p orbitals (2p²).
• C: Highest energy occupied orbital is 2p, which is dumbbell-shaped, not spherical.

Final answer: D