Question

Which does not form a pentahalide?

• A. P
• B. As
• C. Sb
• D. N

Answer 1

Answer: (D)

N

Answer 2

Nitrogen (N) has a valence electron configuration of $2s^2 2p^3$. Its valence shell ($n=2$) lacks vacant d-orbitals. Elements in the second period are restricted by the octet rule and cannot expand their valence shell beyond 8 electrons. Therefore, Nitrogen cannot form pentahalides. Phosphorus (P), Arsenic (As), and Antimony (Sb) are in periods 3, 4, and 5, respectively. They possess vacant d-orbitals in their valence shells, which allows them to expand their octets and form pentahalides (e.g., $PCl_5$).