Isotopes and Relative Formula Mass from Atomic Data

Steps:

• Statement 1: Chlorine's relative atomic mass of 35.5 is not a whole number, indicating an average from multiple isotopes.
• Statement 2: Barium's relative atomic mass of 137 is a whole number, but the word "may" allows for possible isotopes without contradiction.
• Statement 3: Barium chloride is BaCl₂; relative formula mass = 137 + (2 × 35.5) = 137 + 71 = 208.
• All statements align with the given data on atomic masses and periodic group positions.

Why A is correct:

• Relative atomic masses are weighted averages; non-integer values confirm multiple isotopes (Cl), integers permit but do not rule them out (Ba), and formula mass sums atomic masses per chemical formula BaCl₂.

Why the others are wrong:

• B: Excludes statement 2, which is valid due to the permissive "may."
• C: Excludes statement 1, which is confirmed by Cl's non-integer mass.
• D: Excludes statements 1 and 2, both supported by the data.

Final answer: A