Chemistry

Question Analysis
This question involves calculating the average atomic mass of an element with four isotopes, using their respective masses and percent abundances.
The main focus is on applying the weighted average formula, converting percentages to decimals, and summing each isotope’s contribution accurately.

Key Concept Explanation
Average atomic mass = (mass of isotope₁×decimal abundance₁) + (mass of isotope₂×decimal abundance₂) + (mass of isotope₃×decimal abundance₃) + (mass of isotope₄×decimal abundance₄)
Decimal abundance = percent abundance ÷ 100 (converts percentage to proportional value for weighted calculation).

Step-by-step Solution
1. Identify the formula for atomic mass: Atomic Mass = (Mass₁ × %Abundance₁) + (Mass₂ × %Abundance₂) + ...
2. Convert the percent abundances to decimals: 25% → 0.25, 40% → 0.40, 20% → 0.20, 15% → 0.15