Which statement best describes a Bravais lattice?

• A. A finite array of atoms with random positions
• B. An infinite periodic array of points with pure translational symmetry
• C. A single lattice point per unit cell
• D. A structure with no translational symmetry

Answer: (B)

A Bravais lattice is an infinite, periodic grid of points generated by translating a single point through all lattice vectors. This means the pattern looks exactly the same after shifting by any lattice vector, which is pure translational symmetry. In crystals, atoms can sit at those lattice points as a basis, but the lattice itself is just the repeating array of points that fills all of space without end. That’s why descriptions of finite arrays, random positions, or no translational symmetry don’t describe a Bravais lattice. Also, having one lattice point per unit cell isn’t a universal rule—the number of lattice points per unit cell can vary depending on the lattice type.