The 6 pronged octahedral yellow atom represents sulfur in the compound SF6, and is used to depict point group Oh. However, in the nickel arsenide crystal lattice model, it represents arsenic. This atom part is also included in the Class Crystal Structure Models Set.
You can use these Genuine Cochranes of Oxford Orbit Molecular Model Parts to replace missing pieces or augment any of the Orbit Molecular Model Sets & Molecular Model Kits supplied by Indigo Instruments.