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Enzymes function most efficiently at a characteristic optimal pH where their active site shape and charge distribution enable the best substrate binding and catalysis. The experiment shows maximum rate at pH 6, with reduced activity both below (pH 5) and above (pH 7–8). That pattern supports Option B: the enzyme’s optimum is near pH 6. Option A overstates; reduced activity at pH 5 does not prove complete denaturation, just suboptimal conditions. Option C is contradicted by the data—activity at pH 6 is highest, not “only below pH 5.” Option D ignores the clear rate differences across pH values. On GED Science, look for peak-and-decline patterns across a tested range to infer optima (for pH, temperature, or concentration). Always avoid absolute claims (“doesn’t affect,” “only works”) unless data unequivocally show zero activity everywhere else. Recognize that “optimal” means best performance among tested conditions, not exclusive functionality.