Unpaired electrons from odd valence electron count or Lewis structure

Steps:

• Calculate total valence electrons for each molecule.
• Draw Lewis structures to distribute electrons, checking for pairs vs. singles.
• Identify odd total electrons or leftover singles indicating unpaired electron(s).
• Confirm with known molecular properties (paramagnetic if unpaired).

Why A and C are correct:

• NO and NO2 have odd valence electrons (11 and 17), requiring at least one unpaired electron per molecular orbital theory.

Why B is wrong:

• NH3 has 8 valence electrons (even), forming all paired bonds in tetrahedral structure.

Why D is wrong:

• Not enough information (option incomplete).

Final answer: A and C