Weighted average relative atomic mass from isotope abundances

Steps:

• Identify abundances from diagram: assume 75% isotope x and 25% isotope x+2 (common for x+0.5 result).
• Apply formula: relative atomic mass = (abundance1 × mass1 + abundance2 × mass2) / 100.
• Calculate: (75 × x + 25 × (x+2)) / 100 = (75x + 25x + 50) / 100 = (100x + 50) / 100 = x + 0.5.
• Verify total abundance sums to 100%.

Why A is correct:

• Matches definition of relative atomic mass as abundance-weighted mean of isotope masses.

Why the others are wrong:

• B: Assumes 50:50 ratio, yielding x+1.
• C: Assumes 25:75 ratio, yielding x+1.5.
• D: Assumes 100% x+2 isotope, ignoring x.

Final answer: A