Compound X Increases Enzyme Thermostability

Steps:

• Examine the graph: Enzyme activity without compound X drops sharply above 40°C, reaching near 0% by 60°C.
• Compare with X: Activity remains above 60% up to 50°C and higher overall at elevated temperatures.
• Evaluate statement 1: Compound X makes the enzyme more thermostable, as sustained activity at high temperatures confirms stability.
• Assess statements 2 and 3: Statement 2 misinterprets active site changes (no evidence of length alteration); statement 3 incorrectly claims half enzymes form non-standard complexes at 50°C (graph shows ~80% activity with X, not denaturation).

Why C is correct:

• Option C (✓ x x) matches the graph's evidence of improved thermostability without supporting invalid active site or complex claims.

Why the others are wrong:

• A: Incorrectly marks statement 3 as true; no subsidiary complex formation indicated.
• B: Falsely marks statement 1 as wrong; X clearly boosts stability.
• D: Wrongly marks statement 1 as false; data supports thermostability enhancement.

Final answer: C