Final answer:
The false statement about stereoisomers is 'They have identical physical properties,' as enantiomers only have mostly similar properties except for their optical activity, and diastereomers have distinctly different physical properties.
Step-by-step explanation:
The subject of this question is the topic of stereoisomers in chemistry. Among the given options, the false statement regarding stereoisomers is that 'They have identical physical properties.' In reality, stereoisomers, which include enantiomers and diastereomers, may have different physical and chemical properties. Although enantiomers have mostly the same physical and chemical properties, they differ when interacting with chiral substances or environments by displaying opposite optical activities. On the other hand, diastereomers have distinct physical properties such as different melting points, solubilities, and boiling points.
The following statements can be analyzed for truthfulness:
They have the same molecular formula - True, stereoisomers do have the same molecular formula.
They have different spatial arrangements - True, the definition of stereoisomers includes that they have atoms arranged differently in space.
They have identical physical properties - False, as stated before, enantiomers and diastereomers, both types of stereoisomers, can exhibit different physical properties.
They exhibit optical isomerism - True, enantiomers exhibit optical isomerism by rotating plane-polarized light in different directions albeit by the same magnitude.
Therefore, option C 'They have identical physical properties' is the false statement about stereoisomers.