Chemistry

Question Analysis
This question involves solving for an unknown isotope abundance using the weighted average atomic mass formula (two isotopes, one unknown abundance).
The main focus is on setting up a linear equation with a single variable (total abundance = 100%).

Key Concept Explanation
Let % abundance of Br-79 = x → % abundance of Br-81 = 100 - x.
Atomic mass = (m₁×x/100) + (m₂×(100-x)/100)

Step-by-Step Solution
1. Set up the equation:
79.904 = (78.920×x/100) + (80.916×(100 - x)/100)
2. Multiply all terms by 100:
7990.4 = 78.920x + 8091.6 - 80.916x
3. Combine like terms:
7990.4 = 8091.6 - 1.996x
4. Rearrange to solve for x:<...