Final answer:
The best unit cells for square, hexagonal, triangular, and rectangular lattices are a square, hexagon, rhombus, and rectangle respectively.
Step-by-step explanation:
The best unit cell for a square lattice is a square itself. In a square lattice, the lattice points are arranged in a square pattern where each lattice point has four nearest neighbors. For a hexagonal lattice, the best unit cell is a hexagon. In a hexagonal lattice, the lattice points are arranged in a hexagonal pattern where each lattice point has six nearest neighbors. For a triangular lattice, the best unit cell is a rhombus. In a triangular lattice, the lattice points are arranged in a triangular pattern where each lattice point has three nearest neighbors. For a rectangular lattice, the best unit cell is a rectangle. In a rectangular lattice, the lattice points are arranged in a rectangular pattern where each lattice point has four nearest neighbors.