The Correct Answer and Explanation is:
The correct answer is B.
The Lewis structure of hydrogen cyanide (HCN) shows a hydrogen atom bonded to a carbon atom, which is triple bonded to a nitrogen atom. The nitrogen atom has one lone pair of electrons.
To construct a proper Lewis structure for HCN, we begin by counting the total number of valence electrons. Hydrogen contributes 1, carbon contributes 4, and nitrogen contributes 5, giving a total of 10 valence electrons. Carbon is placed in the center because it can form multiple bonds and balance electronegative interactions. Hydrogen is bonded to carbon by a single covalent bond, which uses 2 electrons.
The remaining electrons are used to form a triple bond between carbon and nitrogen. A triple bond consists of six shared electrons. This leaves us with 2 more electrons, which are placed on the nitrogen atom as a lone pair. Every atom now has a complete valence shell. Hydrogen has 2 electrons, which satisfies its duet requirement. Carbon shares 8 electrons through the bonds. Nitrogen also ends up with 8 electrons, counting the lone pair and the shared electrons in the triple bond.
This arrangement fulfills the octet rule and results in the most stable configuration. Carbon and nitrogen reach full outer shells through bonding, and formal charges are minimized. No lone pairs appear on carbon because all its electrons are involved in bonding, while nitrogen holds a single lone pair.
In contrast, the other choices are incorrect. Option A omits necessary lone pairs. Option C shows only one lone pair but misplaces it, and option D adds a lone pair to carbon, violating bonding norms for that element in this context. Therefore, Option B, which displays H–C≡N with a lone pair on nitrogen, is the correct Lewis structure.
