Chemistry

Question Analysis
This question involves calculating the percent abundance of an isotope using the weighted average atomic mass formula (two isotopes, one unknown abundance).
The main focus is on setting up and solving a linear equation to find the abundance of Li-7.

Key Concept Explanation
Let % abundance of Li-7 = x → % abundance of Li-6 = 100 - x.
Atomic mass = (m₁×x/100) + (m₂×(100-x)/100)

Step-by-Step Solution
1. Set up the equation using the given values:
6.941 = (7.016×x/100) + (6.015×(100 - x)/100)
2. Multiply all terms by 100 to eliminate denominators:
694.1 = 7.016x + 6.015(100 - x)
3. Expand the right-hand side:
694.1 = 7.016x + 601.5 - 6.015x
4. Combine like terms (7.016x - 6.015x = 1.001x):