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 (since total abundance = 100%).

Key Concept Explanation
Let % abundance of B-10 = x → % abundance of B-11 = 100 - x (total abundance = 100%).
Atomic mass = (m₁×x/100) + (m₂×(100-x)/100)

Step-by-Step Solution
Step 1: Define variables
Let the fraction of B-10 be (x). Then the fraction of B-11 is (1 - x).
The atomic mass formula is:

We know:

Step 2: Expand

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