What is the coordination number of each sphere in a two-dimensional hexagonal close-packed structure?

Which of the following statements is incorrect?

The unit cell of a $NaCl$ lattice:

In an alloy of metals $M$ and $N$,$N$ atoms form a $bcc$ structure,while $M$ atoms occupy the center of each face. If the cube is cut such that all atoms along one body diagonal are removed,the formula of the resulting solid will be ...........

In a face-centered cubic lattice,a unit cell is shared equally by how many unit cells?

$A$ cubic structure is formed where atoms of element $X$ are occupied at the corners of the cube and also at the face centers. Atoms of element $Y$ are present at the body center and at the edge centers. If all the atoms are removed along a plane passing through the middle of the cube (bisecting the four edges), the formula will become