Final answer:
Nitrogen can form triple bonds because it has valence d orbitals, while phosphorus can only form three single bonds as it lacks valence d orbitals.
Step-by-step explanation:
The nitrogen atom can form triple bonds due to the presence of its valence d orbitals, which allows it to form sp² hybrid orbitals. These hybrid orbitals can overlap with the hybrid orbitals of another nitrogen atom, resulting in the formation of a triple bond. On the other hand, phosphorus does not have valence d orbitals, so it can only form three single bonds by utilizing its sp³ hybrid orbitals.