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The coordination number of a sphere occupying tetrahedral hole is 4. They are smaller than the cubic or octahedral holes. The face centred cubic arrangement has both tetrahedral (8) and octahedral holes (4). A good example of a tetrahedral structure is methane. Here, the carbon atom is attached to four equidistance hydrogen atoms placed at the corners of tetrahedrons.

Octahedron is defined as a polyhedron with 8 regular triangles. It is made by one sphere surrounded by 6 equal spheres. By connecting 6 centres of the surrounding spheres, octahedron can be generated. A good example is sodium chloride. Here, octahedral holes are formed by chloride ions which are occupied by smaller sodium ions. In a face centred cube, there are four octahedral holes, with one octahedral hole per anion.

An octahedral hole occupies a larger size than tetrahedral holes. Hence, the larger anion occupies by the larger cation to fit the octahedral hole. Among the provided elements the larger size atom is \({\rm{Ca}}\) as it belongs to the \({4^{{\rm{th }}}}\) period of elements (from top to bottom the size of atoms increases).

Therefore, calcium mostly likely reacts with sulfur to form a solid.