Chemistry

Question Analysis
This question involves calculating the average atomic mass of element Z with three isotopes, using their given masses and percent abundances.
The main focus is on applying the weighted average formula by 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)
Decimal abundance = percent abundance ÷ 100 (converts percentage to a proportional value for the weighted average).

Step-by-step Solution
1. Identify the masses and abundances of the isotopes:
Isotope Z-20: Mass = 19.97 amu, Abundance = 40% (0.40 in decimal form)
Isotope Z-21: Mass = 20.97 amu, Abundance = 30% (0.30 in decimal form)
Isotope Z-22: Mass = 21.97 amu, Abundance = 30% (0.30 in decimal form)
2. Use the formula for atomic mass: Atomic Mass = (Mass₁ ...