#### Which of the following statements is not true for the crystal structure of cesium chloride $(CsCl)$?Option: 1 $CsCl$ has a cubic structure.Option: 2 $Cs^+$ and $Cl^-$ ions are arranged in a face-centred cubic lattice.  Option: 3 $Cs^+$ and $Cl^-$ ions have a coordination number of 8 and 6, respectively.Option: 4 The $Cs^+$ ions are located at the corners of the cube and $Cl^-$ ions are at the center of the cube.

$CsCl$ is an example of a simple cubic crystal lattice, not a face-centred cubic lattice as stated in option 2. In a simple cubic lattice, the unit cell consists of a cube with lattice points located at the corners of the cube. Each lattice point represents one $Cs^+$ ion. Additionally, there is one $Cl^-$ ion located at the centre of the cube.

In $CsCl$, each $Cs^+$ion is surrounded by $8\ Cl^-$ ions arranged at the corners of a cube around it, resulting in a coordination number of 8 for the $Cs^+$ ion. On the other hand, each $Cl^-$ ion is surrounded by $6\ Cs^+$ ions arranged at the corners of an octahedron around it, resulting in a coordination number of 6 for the $Cl^-$ ion. This is stated in option 3.

Therefore, the correct statement regarding the location of $Cs^+$ and $Cl^-$ ions in the $CsCl$ crystal structure is that $Cs^+$ ions are located at the corners of the cube and $Cl^-$ ions are located at the centre of the cube.

Option 4) incorrectly describes the location of the $Cl^-$ ion in the $CsCl$ unit cell.