Monitoring reaction rate via mass loss from volatile product

Steps:

• Analyze the equation: No gaseous products formed, only Br₂(aq) and H₂O(l).
• Assess gas syringe: Cannot measure volume change without gas production.
• Assess pH meter: H⁺ consumption causes pH rise, but logarithmic scale complicates linear rate calculation.
• Assess balance: Volatile Br₂ evaporates in open system, causing measurable mass loss proportional to reaction progress.

Why D is correct:

• Balance tracks mass loss rate, directly tied to Br₂ production stoichiometry (3 mol Br₂ per reaction), allowing rate determination via Δm/Δt.

Why the others are wrong:

• A: Includes unsuitable gas syringe and imprecise pH monitoring.
• B: Gas syringe useless without gas evolution.
• C: pH meter's nonlinear response hinders accurate rate variation over time.

Final answer: D