Final answer:
Enzymes are most active at their optimum pH, which is often around the biological pH of 7.4. Since pH 7.0 is the closest to this median value, it is likely the pH at which 80% of enzymes would be active.
Step-by-step explanation:
To determine at what pH 80% of the enzymes will be in an active state, we need to consider the optimum pH specific to the enzyme in question. Enzymes generally achieve their maximum activity at their optimum pH, which for most enzymes falls near the biological pH of 7.4. However, the activity begins to decrease when the pH deviates significantly from the optimum level; enzymes can be denatured at extremely high or low pH values.
Based on the provided options, since we are looking for a state where 80% of the enzymes are active, we can conclude that the pH value closest to the median of the optimum pH range will be the best answer. In this case, given that the overall range of optimal pH for most body enzymes is between 6 and 8, pH 7.0 (option d) would likely be the pH at which 80% of the enzymes are in an active state because it is closest to the median of the typical range.