The correct answer is $\boxed{\text{C}}$.
NaCl is an ionic crystal, which means that it is made up of positively charged sodium ions and negatively charged chloride ions. The ions are arranged in a cubic structure, with each sodium ion surrounded by six chloride ions and each chloride ion surrounded by six sodium ions. This arrangement is called an octahedral crystal structure.
A body centered cubic (bcc) crystal structure is a cubic crystal structure in which each lattice point is occupied by an atom. The atoms are arranged in a cubic lattice with an atom at the center of each cube.
A face centered cubic (fcc) crystal structure is a cubic crystal structure in which each lattice point is occupied by an atom. The atoms are arranged in a cubic lattice with an atom at the center of each face of the cube.
A square planar crystal structure is a crystal structure in which the atoms are arranged in a square planar lattice. The atoms are bonded to each other in a way that forms a square with four atoms at the corners and one atom in the center.
In conclusion, the structure of NaCl crystal is octahedral.