Final answer:
Diastereoisomers have different physical and chemical properties and do not have to all be optically active, unlike enantiomers which share the same properties except in chiral environments.
Step-by-step explanation:
The properties of diastereoisomers include having different physical and chemical properties, not being mirror images, and having R & S configuration at least in one stereocentre. However, not all diastereoisomers have to be optically active. A molecule can have more than one stereocenter and still be optically inactive if it is a meso compound, which has a plane of symmetry.
Therefore, the statement that is false is that diastereoisomers have the same physical and chemical properties - this characteristic actually pertains to enantiomers or optical isomers when not interacting with chiral substances.