Enzyme activity decreases substrate concentration most at optimal pH

Steps:

• Enzyme functions best at pH 1-2, converting most substrate to product in 5 minutes.
• At optimal pH, remaining substrate is lowest due to highest reaction rate.
• As pH increases beyond 2, enzyme activity drops, leaving more substrate unreacted.
• Graph of remaining substrate vs. pH shows a minimum at pH 1-2, then rises to pH 8.

Why A is correct:

• A depicts lowest remaining substrate at pH 1-2 (optimal activity) with levels increasing at higher pH, matching enzyme kinetics where rate = k [E][S] peaks in acidic conditions.

Why the others are wrong:

• B likely shows decreasing substrate with rising pH, inverting the activity trend.
• C probably peaks substrate remaining at low pH, ignoring optimal activity.
• D may show flat or unrelated pattern, not reflecting pH dependence.

Final answer: A