Higher acid concentration speeds up the reaction and increases total gas yield Steps:

• Compare data: Experiment 2 shows faster initial gas production (30 cm³ vs. 20 cm³ at 20 s) and higher volume at 60 s (75 cm³ vs. 60 cm³), with rate slowing to match experiment 1 later.
• Reaction rate depends on [HCl] and CaCO₃ surface area; total CO₂ volume equals moles of acid (excess CaCO₃).
• Faster rate and higher volume at fixed time indicate increased [HCl], raising both rate and total yield.
• Other changes either match rate (A) or increase rate without raising total yield (C, D).

Why B is correct:

• Higher [HCl] increases collision frequency (collision theory), accelerating rate; same 100 cm³ volume means more moles, yielding more CO₂.

Why the others are wrong:

• A: Same [HCl] keeps initial rate unchanged, though total yield rises; data shows faster rate.
• C: Greater surface area speeds rate but total yield unchanged (same acid moles).
• D: Higher temperature boosts rate (Arrhenius equation) but total yield unchanged.

Final answer: B