{"knowledge_schema": {"broad_category": "Crystallography \u2192 Symmetry in Crystals \u2192 Optical Activity", "refinement": "This problem focuses on identifying crystal classes that are achiral and non-polar while possessing the symmetry necessary for optical activity.", "specific_scope": "The task is to evaluate the given candidates based on their symmetry properties to determine which classes meet the criteria for optical activity without being chiral or polar.", "goal": "Identify the correct achiral and non-polar crystal classes that exhibit the necessary symmetry for optical activity."}, "summary": "The problem involves identifying specific crystal classes that are both achiral and non-polar, yet possess the symmetry required for optical activity. The candidates provided must be analyzed based on their symmetry properties to determine which ones fit the criteria. The goal is to select the correct classes that align with the requirements of optical activity while ensuring they do not exhibit chirality or polarity."}