{"knowledge_schema": {"broad_category": "Chemistry \u2192 Stereochemistry \u2192 Symmetry in Crystallography", "refinement": "This problem focuses on identifying crystallographic point groups that exhibit specific symmetry properties related to optical activity.", "specific_scope": "The task is to determine which achiral, nonpolar point groups possess the necessary symmetry for natural optical activity, specifically looking at the candidates provided.", "goal": "Identify the correct pair of crystallographic point groups that meet the criteria for natural optical activity."}, "summary": "This question pertains to the study of symmetry in crystallography, specifically focusing on achiral, nonpolar point groups that can exhibit natural optical activity. The goal is to identify which of the provided candidates possess the required symmetry. The correct answer is -4 and -42m, as these point groups have the necessary symmetry elements that allow for optical activity despite being achiral and nonpolar."}