Percent yield via mass ratio; relative rate via leaving group ability Steps:

• Compute percent yield for reaction 1: (12.3 g product / 18 g reactant) × 100 ≈ 68% (rounded to 70% in choices).
• Identify reactions: Both tertiary halides undergo E2/SN1-E1 with hot aq NaOH, yielding 2-methylbut-2-ene (X).
• Compare rates: Leaving group Br⁻ (reaction 1) departs faster than Cl⁻ (reaction 2) due to weaker C-Br bond and better stabilization.
• Select option: 70% yield with reaction 1 faster matches data.

Why C is correct:

• Aligns with mass-based yield calculation and SN1/E2 rate law emphasizing leaving group (Br > Cl).

Why the others are wrong:

• A: Incorrect yield (41% mismatches 70% calculation).
• B: Incorrect yield (41%) and relative rate (Cl⁻ poorer leaving group than Br⁻).
• D: Incorrect relative rate (reaction 2 slower, not faster).

Final answer: C