Final answer:
In a cubic closest packed (face-centered cubic) structure, the coordination number of a nickel atom is 12, indicating that each nickel atom is surrounded by twelve other nickel atoms. The correct option is D.
Step-by-step explanation:
The cubic closest packed structure, also known as the face-centered cubic (fcc) structure, refers to a lattice arrangement where each atom is surrounded by 12 other atoms. This gives an atom in an fcc crystal structure a coordination number of 12.
In contrast, the body-centered cubic (bcc) structure, has a coordination number of 8, as atoms are surrounded by 8 others. However, it's important to note that for coordination chemistry involving complex ions and ligands, the coordination number might count the number of bonds, not necessarily the number of surrounding atoms, as might be seen in some nickel complexes.