The body-centered cubic system has a lattice point at each of the eight corner points of the unit cell plus one lattice point in the centre. Thus it has a net total of 2 lattice points per unit cell ( 1⁄8 × 8 + 1).The face-centered cubic system has lattice points on the faces of the cube, that each gives exactly one half contribution, in addition to the corner lattice points, giving a total of 4 lattice points per unit cell ( 1⁄8 × 8 from the corners plus  1⁄2 × 6 from the faces).
Simple reason - It violates the cubic symmetry. To see it from another perspective - Base centered cubic lattice is equivalent to a simple tetragonal lattice. Draw two unit cells adjacent to each other. Then connect the base center points to the corener points which are shared by these two unit cells. Then connect the two base centered point in each unit cell. Now you have a simple tetragonal lattice. Simple tetragonal lattice has one lattice point per unit cell compared to two lattice point per unit cell of base centered lattice. Always the lower lattice point lattice is considered for a given symmetry. Because of symmetry breaking, the symmetry of base centered cubic lattice is same as tetragonal lattice.
The unit cell is the fundamental unit of a crystal lattice, it is like the shapes used up to make the tessellations one makes in math class. The unit cell is therefore the subunit of the crystal lattice.
To calculate the number of atoms in a unit cell, you first determine the type of unit cell (simple cubic, body-centered cubic, or face-centered cubic) and the number of atoms contributed by each lattice point. Then, you multiply the number of lattice points within the unit cell by the number of atoms contributed per lattice point. For example, a simple cubic unit cell has one atom per lattice point, so the total number of atoms in a simple cubic unit cell would be 1 x 1 = 1 atom.
The unit cell is the smallest portion of a crystal lattice that reveals the three-dimensional pattern. It is a repeating structure that, when repeated in all directions, forms the entire crystal lattice.
Primitive unit cells use every lattice point as a unit cell vertex.Non-primitive unit cells, however, contain extra lattice points not at the corners.
The body-centered cubic system has a lattice point at each of the eight corner points of the unit cell plus one lattice point in the centre. Thus it has a net total of 2 lattice points per unit cell ( 1⁄8 × 8 + 1).The face-centered cubic system has lattice points on the faces of the cube, that each gives exactly one half contribution, in addition to the corner lattice points, giving a total of 4 lattice points per unit cell ( 1⁄8 × 8 from the corners plus  1⁄2 × 6 from the faces).
When a unit in a crystal lattice has lattice points only at its corners ,it is called a simple or primitive unit cell. There are seven types of primitive unit cells among crystal.They are 1. Cubic unit cell 2. Tetragonal unit cell 3. Orthorhombic unit cell 4. Monoclinic unit cell 5. Rhombohedral unit cell 6. Triclinic unit cell 7. Hexagonal unit cell And, the smallest repeating unit in space lattice which when repeated over and over again produces the complete space lattice.This is called unit cell. In easy form , The unit cell which do not contain any interior point are called primitive unit cell.
when constituent particles are present only on the corner positions of a unit cell , it is called as Primitive unit cell .
In a single unit cell of a NaCl crystal lattice, there are four composite Cl- ions.
In a single unit cell of a NaCl crystal lattice, there are six composite Na ions present.
Simple reason - It violates the cubic symmetry. To see it from another perspective - Base centered cubic lattice is equivalent to a simple tetragonal lattice. Draw two unit cells adjacent to each other. Then connect the base center points to the corener points which are shared by these two unit cells. Then connect the two base centered point in each unit cell. Now you have a simple tetragonal lattice. Simple tetragonal lattice has one lattice point per unit cell compared to two lattice point per unit cell of base centered lattice. Always the lower lattice point lattice is considered for a given symmetry. Because of symmetry breaking, the symmetry of base centered cubic lattice is same as tetragonal lattice.
The unit cell is the fundamental unit of a crystal lattice, it is like the shapes used up to make the tessellations one makes in math class. The unit cell is therefore the subunit of the crystal lattice.
To calculate the number of atoms in a unit cell, you first determine the type of unit cell (simple cubic, body-centered cubic, or face-centered cubic) and the number of atoms contributed by each lattice point. Then, you multiply the number of lattice points within the unit cell by the number of atoms contributed per lattice point. For example, a simple cubic unit cell has one atom per lattice point, so the total number of atoms in a simple cubic unit cell would be 1 x 1 = 1 atom.
. A crystal structure is composed of a pattern, a set of atoms arranged in a particular way, and a lattice exhibiting long-range order and symmetry. Patterns are located upon the points of a lattice, which is an array of points repeating periodically in three dimensions
The unit cell is the smallest portion of a crystal lattice that reveals the three-dimensional pattern. It is a repeating structure that, when repeated in all directions, forms the entire crystal lattice.
The repeating group of atoms in a crystal is called a unit cell. This unit cell is the smallest repeating structure that can be used to build up the entire crystal lattice.