Final answer:
Only phosphorus (P) out of the given options is capable of forming triple bonds because it has the necessary p orbitals and can achieve the appropriate hybridization.
Step-by-step explanation:
The question asks which of the following atoms are capable of forming triple bonds: H, P, Si, S. The ability to form triple bonds is generally associated with the presence of p orbitals that can hybridize to form pi bonds in addition to a sigma bond. Hydrogen (H) is not capable of forming triple bonds as it can only form a single covalent bond. Silicon (Si) typically forms single bonds due to its preference for sp3 hybridization and the difficulty in forming multiple bonds with itself. Sulfur (S) can form two double bonds or a single double bond but forming triple bonds is not common due to its electron configuration and size. Phosphorus (P), however, can form triple bonds as in the case of the P2 molecule, although this is less common than nitrogen due to the larger size and less efficient p orbital overlap in the third period elements.
Therefore, the answer is (b) Phosphorus (P) is capable of forming triple bonds.