Final answer:
The lone pair electrons on the nitrogen atom are contained in an sp hybridized orbital, specifically labeled as 2sp. This accounts for the linear geometry of nitrogen in compounds with a triple bond, where one sp orbital forms a bond and the other contains the lone pair.
Step-by-step explanation:
The lone pair electrons on the nitrogen (N) atom are contained in an sp hybridized orbital. According to the molecular orbital theory, an sp hybridized orbital is linear in geometry and in the case of nitrogen, one of the sp orbitals would form a σ-bond, while the other contains the lone pair of electrons. The three 2p orbitals on a nitrogen atom are typically used to form π-bonds in cases of multiple bonding such as a triple bond in nitriles or cyanides, where the nitrogen has a linear structure, or double bonding as found in other nitrogen compounds like imines.
For the given compound where nitrogen has a triple bond (as illustrated in diagrams for hydrogen cyanide and similar molecules), the lone pair of electrons would be in the sp hybridized orbital that is not involved in the σ-bonding. Consequently, the correct answer to identify the atomic orbital containing the lone pair electrons on the nitrogen atom is D. 2sp.