Final answer:
The statement that to obtain pure crystals, the crystal lattice structure should contain molecules of various types is false. Pure crystals require a consistent and regular lattice structure of identical molecules or atoms.
Step-by-step explanation:
To obtain pure crystals, the crystal lattice structure should not contain molecules of various types; rather, it should consist of a regular, repeating unit of identical molecules or atoms. The statement 'To obtain pure crystals, the crystal lattice structure should contain molecules of various types' is false. The purity of a crystal is defined by the regularity and consistency of its lattice structure. For instance, molecular crystals consist of molecules at the lattice points of the crystal, held together by intermolecular forces such as dispersion forces, dipole-dipole forces, or hydrogen bonds in the case of ice. These intermolecular forces are weaker than the ionic or covalent bonds found in other types of crystals.
In a pure crystalline solid, the unit cells repeat the same structure throughout the crystal, and this is what contributes to their unique properties, such as distinct melting points. Any inclusion of different molecules within the crystal lattice would disrupt the purity and potentially alter significant physical properties like melting point, electrical conductivity, and hardness.