Explanation:

BCC structure:
The body-centered cubic (BCC) structure is a type of crystal structure in which the lattice points are located at the corners and at the center of the cube. In this structure, each atom or ion is surrounded by eight nearest neighboring atoms or ions.

Identification of BCC Structures:
To identify whether a compound has a BCC structure, we need to analyze the arrangement of atoms or ions in its crystal lattice.

Analysis of the Given Options:

a) MgO:
MgO does not have a BCC structure. It has a rock salt (NaCl) structure, which is a type of face-centered cubic (FCC) structure. In an FCC structure, the lattice points are located at the corners and at the center of each face of the cube.

b) CsCl:
CsCl (Cesium Chloride) has a BCC crystal structure. In the CsCl structure, the cesium ions are located at the corners of the cube, while the chloride ions are located at the center of the cube. This arrangement follows the body-centered cubic structure.

c) MnO:
MnO does not have a BCC structure. It has a rock salt (NaCl) structure, similar to MgO. The manganese ions are located at the corners of the cube, and the oxygen ions are located at the center of each face of the cube.

d) NaCl:
NaCl (Sodium Chloride) does not have a BCC structure. It also has a rock salt (NaCl) structure, where the sodium ions are located at the corners of the cube, and the chloride ions are located at the center of each face of the cube.

Conclusion:
Among the given options, CsCl is the only compound that has a BCC crystal structure. The other compounds (MgO, MnO, and NaCl) have different crystal structures.