Chlorine mass spectrum analysis

Steps:

• Identify peaks in chlorine spectrum: typically molecular ions at m/z 70 (^{35}Cl_2), 72 (^{35}Cl^{37}Cl), 74 (^{37}Cl_2), with possible monomer peaks at 35 and 37.
• For statement 1: Use all five peaks' m/z and abundances to compute weighted average for relative atomic mass via formula (sum of (abundance × m/z)/total abundance).
• For statement 2: Peak Z (likely m/z 74) corresponds to heaviest isotope; given quantity (3.01 × 10^{20} molecules) matches sample size calculation using Avogadro's number and abundance.
• For statement 3: Subset peaks X, Y, Z (molecular ions) suffice for atomic mass calculation, as their ratios reflect isotopic abundances directly.

Why A is correct:

• All statements align with mass spectrometry principles: atomic mass from isotopic data (statement 1 and 3), molecule count from abundance and sample mass (statement 2).

Why the others are wrong:

• B omits valid statement 3 on subset peak calculation.
• C omits valid statement 2 on molecule quantification.
• D omits valid statement 1 on full spectrum use.

Final answer: A