Unpaired electrons indicate radical species

Steps:

• Count total valence electrons to check for odd numbers, signaling unpaired electrons.
• NO: 5 (N) + 6 (O) = 11 electrons, but forms stable bonds with all paired.
• NH: 5 (N) + 1 (H) = 6 electrons, odd total.
• NH3: 5 (N) + 3 (H) = 8 electrons, even total.
• Option D provides no molecule, so not enough information.

Why B is correct:

• NH has an odd number of valence electrons (6 total), requiring at least one unpaired electron by the Pauli exclusion principle and Lewis dot rules for radicals.

Why the others are wrong:

• A. NO pairs all electrons in its double bond Lewis structure, forming a stable molecule without unpaired electrons.
• C. NH3 has an even number of valence electrons (8 total), allowing all to pair in three N-H bonds and one lone pair.
• D. Not enough information.

Final answer: B