Final answer:
The coordination number of an aluminum atom in the face-centered cubic structure of aluminum is 12, which indicates that each aluminum atom has 12 nearest neighboring atoms. The correct option d.
Step-by-step explanation:
The coordination number of an atom in a crystal structure refers to the number of other atoms it directly touches. For aluminum in a face-centered cubic (FCC) structure, the coordination number is determined by the number of nearest neighbors that each aluminum atom has.
In an FCC structure, atoms are located at each corner of the cube and at the centers of each of its faces. Each atom at the corner of a cubic unit cell touches four atoms on the face centers of the cube (along the face diagonal), therefore having 12 nearest neighbors.
Hence, the coordination number of an aluminum atom in the face-centered cubic structure of aluminum is 12. The correct option d.